Clutchlog — versatile (de)clutchable spatial logging
====================================================

**Clutchlog is a *spatial* logging system that targets versatile *debugging*.**
**It allows to (de)clutch messages for a given: log level, source code location or call stack depth.**

- [Project page on Github](https://github.com/nojhan/clutchlog)
- [Documentation](https://nojhan.github.io/clutchlog/)

<p align="center">
    <img
        alt"Clutchlog logo"
        src="https://raw.githubusercontent.com/nojhan/clutchlog/master/docs/clutchlog_logo.svg"
        width="400"
    />
</p>

[TOC]

Features
--------

Clutchlog allows to select which log messages will be displayed, based on their locations:

- **Classical log levels**: each message has a given detail level and it is displayed if you ask for a at least the same
  one.
- **Call stack depth**: you can ask to display messages within functions that are called up to a given stack depth.
- **Source code location**: you can ask to display messages called from given files, functions and line number, all based on
  regular expressions.

Additionally, Clutchlog will do its best to allow the compiler to optimize out calls,
for instance debug messages in "Release" builds.

Additional features:

- **Templated log format**, to easily design your own format.
- **Colored log**. By default only important ones are colored (critical and error in red, warning in magenta).
- **Macro to dump the content of a container in a file** with automatic naming (yes, it is useful for fast debugging).
- **Generic clutching wrapper**, to wrap any function call. Useful to (de)clutch *asserts* for example.


Example
-------

Adding a message is a simple as calling a macro (which is declutched in Debug build type, when `NDEBUG` is not defined):
```cpp
CLUTCHLOG(info, "matrix size: " << m << "x" << n);
```

To configure the display, you indicate the three types of locations, for example in your `main` function:
```cpp
    auto& log = clutchlog::logger();
    log.depth(2);                          // Log functions called from "main" but not below.
    log.threshold("Info"); // Log only "info", "warning", "error" or "critical" messages.
    log.file("algebra/.*");                // Will match any file in the "algebra" directory.
    log.func("(mul|add|sub|div)");         // Will match "multiply", for instance.
```

Example of a real-life log session (as seen in the [frictionlesser](https://github.com/jdreo/frictionlesser) software):

![A log screen capture with full details, showing colored messages and location.](https://raw.githubusercontent.com/nojhan/clutchlog/master/demo.png)

Demo showing fancy styling:

![A log screen capture showing fancy coloring of text lines.](https://raw.githubusercontent.com/nojhan/clutchlog/master/demo-extra.png)

For more detailled examples, see the "Usage" sections below and the `tests` directory.


Rationale
---------

Most of existing logging systems targets service events storage, like fast queuing of transactions in a round-robin
database.
Their aim is to provide a simple interface to efficiently store messages somewhere, which is appropriated when you have
a well known service running and you want to be able to trace complex users interactions across its states.

Clutchlog, however, targets the *debugging* of a (typically single-run) program.
While you develop your software, it's common practice to output several detailled informations on the internal states
around the feature you are currently programming.
However, once the feature is up and running, those detailled informations are only useful if you encounter a bug
traversing this specific part.

While tracing a bug, it is tedious to uncomment old debugging code (and go on the build-test cycle)
or to set up a full debugger session that displays all appropriate data (with ad-hoc fancy hooks).

To solve this problem, Clutchlog allows to disengage *at runtime* your debug log messages in various parts of the program,
allowing for the fast tracking of a bug across the execution.


Basic Usage
===========


Calls
-----

The main entrypoint is the `CLUTCHLOG` macro, which takes the desired log level and message.
The message can be anything that can be output in an `ostringstream`.
```cpp
// Simple string:
CLUTCHLOG(info, "hello world");

// Serialisable variable:
double value = 0;
CLUTCHLOG(error, value);

// passed using inline output stream operators:
CLUTCHLOG(debug, "hello " << value << " world");
```

There is also a macro to dump the content of an iterable within a separate file: `CLUTCHDUMP`.
This function takes care of incrementing a numeric suffix in the file name,
if an existing file with this name exists.
```cpp
std::vector<int> v(10);
std::generate(v.begin(), v.end(), std::rand);
CLUTCHDUMP(debug, vec, "test_{n}.dat");
/* Will output in cat "rand_0.dat"
* # [t-dump] Info in main (at depth 5) @ /home/nojhan/code/clutchlog/tests/t-dump.cpp:22
* 1804289383
* 846930886
* 1681692777
*/
```
Note that if you pass a file name without the `{n}` tag, the file will be overwritten as is.


Log level semantics
-------------------

Log levels use a classical semantics for a human skilled in the art, in decreasing order of importance:

- *Critical*: an error that cannot be recovered. For instance, something which will make a server stop right here.
- *Error*: an error that invalidates a function, but may still be recovered. For example, a bad user input that will make a server reset its state, but not crash.
- *Warning*: something that is strange, but is probably legit. For example a default parameter is set because the user forgot to indicate its preference.
- *Progress*: the state at which computation currently is.
- *Note*: some state worth noting to understand what's going on.
- *Info*: any information that would help ensuring that everything is going well.
- *Debug*: data that would help debugging the program if there was a bug later on.
- *XDebug*: debugging information that would be heavy to read.

Note: the log levels constants are lower case (for example: `clutchlog::level::xdebug`), but their string representation is not (e.g. "XDebug", this should be taken into account when using `clutchlog::threshold` or `clutchlog::level_of`).


Location filtering
------------------

To configure the global behaviour of the logger, you must first get a reference on its (singleton) instance:
```cpp
auto& log = clutchlog::logger();
```

One can configure the location(s) at which messages should actually be logged:
```cpp
log.depth(3); // Depth of the call stack, defaults to the maximum possible value.
log.threshold(clutchlog::level::error); // Log level, defaults to error.
```
Current levels are defined in an enumeration as `clutchlog::level`:
```cpp
enum level {critical=0, error=1, warning=2, progress=3, note=4, info=5, debug=6, xdebug=7};
```

File, function and line filters are indicated using (ECMAScript) regular expressions:
```cpp
log.file(".*"); // File location, defaults to any.
log.func(".*"); // Function location, defaults to any.
log.line(".*"); // Line location, defaults to any.
```
A shortcut function can be used to filter all at once:
```cpp
log.location(file, func, line); // Defaults to any, second and last parameters being optional.
```

Strings may be used to set up the threshold:
```cpp
log.threshold("Error"); // You have to know the exact —case sensitive— string.
```
Note that the case of the log levels strings matters (see below).


Output Configuration
--------------------

The output stream can be configured using the `clutchlog::out` method:
```cpp
log.out(std::clog); // Defaults to clog.
```

The format of the messages can be defined with the `clutchlog::format` method, passing a string with standardized tags surrounded by `{}`:
```cpp
log.format("{msg}");
```
Available tags are:

- `{msg}`: the logged message,
- `{level}`: the current log level (i.e. `Critical`, `Error`, `Warning`, `Progress`, `Note`, `Info`, `Debug` or `XDebug`),
- `{level_letter}`: the first letter of the current log level,
- `{level_short}`: the current log level, printed in only four letters,
- `{file}`: the current file (absolute path),
- `{func}`: the current function,
- `{line}`: the current line number,
- `{level_fmt}`: the style of the current level (i.e. configured with `clutchlog::style`),
- `{filehash_fmt}`: a style for file names, which is value-dependant (see `clutchlog::filehash_styles`),
- `{funchash_fmt}`: a style for function names, which is value-dependant (see `clutchlog::funchash_styles`).

Some tags are only available on POSIX operating systems as of now:
- `{name}`: the name of the current binary,
- `{depth}`: the current depth of the call stack,
- `{depth_marks}`: as many chevrons `>` as there is calls in the stack,
- `{depth_fmt}`: a style depending on the current depth value (see `clutchlog::depth_styles`),
- `{hfill}`: Inserts a sequence of characters that will stretch to fill the space available
  in the current terminal, between the rightmost and leftmost part of the log message.


### Log Format

The default log format is `"[{name}] {level_letter}:{depth_marks} {msg} {hfill} {func} @ {file}:{line}\n"`,
it can be overriden at compile time by defining the `CLUTCHLOG_DEFAULT_FORMAT` macro.

By default, and if `CLUTCHLOG_DEFAULT_FORMAT` is not defined,
clutchlog will not put the location-related tags in the message formats
(i.e. `{name}`, `{func}`, and `{line}`) when not in Debug builds.


Output Styling
--------------

Output lines can be styled differently depending on their content.

For example, output lines can be colored differently depending on the log level.
```cpp
// Print error messages in bold red:
log.style(level::error, // First, the log level.
    fmt::fg::red,       // Then the styles, in any order...
    fmt::typo::bold);
```

Or, if you want to declare some semantics beforehand:
```cpp
// Print warning messages in bold magenta:
using fmt = clutchlog::fmt;
fmt warn(fmt::fg::magenta, fmt::typo::bold);
log.style(level::warning, warn);
```

Note: this inserts a style marker at the very beginning of the line.
If you add other styles later on the line, they will take precedence.

Colors can be specified in several different ways.
The ANSI color mode will be automatically detected,
depending on the types of arguments passed to styling functions:
- named tags from `clutchlog::fmt::fg` or `clutchlog::fmt::bg` will encode a 16-colors mode,
- integers will encode a 256-colors mode,
- numeric triplets or web hex strings will encode a 16 million ("true") colors mode,
- `clutchlog::fg::none` and `clutchlog::bg::none` can be passed in all modes.

For example, all the following lines encode
a bright red foreground for the critical level
(see the "Colors" section below):
```cpp
    log.style(level:critical,
        fmt::fg::red); // 16-colors mode.
    log.style(level:critical,
        255); // 256-colors mode.
    log.style(level:critical,
        255,0,0); // 16M-colors mode.
    log.style(level:critical,
        "#ff0000"); // 16M-colors mode again.
```

You may use styling within the format message template itself, to add even more colors:
```cpp
using fmt = clutchlog::fmt;
std::ostringstream format;
fmt discreet(fmt::fg::blue);
format << "{level}: "
    << discreet("{file}:") // Used as a function (inserts a reset at the end).
    << fmt(fmt::fg::yellow) << "{line}" // Used as a tag (no reset inserted).
    << fmt(fmt::typo::reset) << " {msg}" << std::endl; // This is a reset.
log.format(format.str());
```
Note: messages at the "critical", "error" and "warning" log levels are colored by default.
You may want to set their style to `none` if you want to stay in control of inserted colors in the format template.

The horizontal filling line (the `{hfill}` tag) can be configured separately with `clutchlog::hfill_style`,
for example:
```cpp
    log.hfill_style(fmt::fg::black);
```
Note: this will actually reset any styling after the hfill,
disabling any style you would have set for the whole message using `clutchlog::format`
for the remaining of the message.


### Typographic Style

Available typographies:

- reset (remove any style),
- bold,
- underline,
- inverse,
- none.

Typographic styles are always passed with the named tag
(see `clutchlog::fmt::typo`), whatever the color mode.


### Colors

#### 16-colors mode

Using the `clutchlog::fmt` class, you can style:

- the foreground color, passing a `clutchlog::fmt::fg`,
- the background color, passing a `clutchlog::fmt::bg`.

In 16-colors mode, any of the arguments may be passed, in any order,
if an argument is omitted, it defaults to no color/style.

Available colors are:

- black,
- red,
- green,
- yellow,
- blue,
- magenta,
- cyan,
- white,
- bright_black,
- bright_red,
- bright_green,
- bright_yellow,
- bright_blue,
- bright_magenta,
- bright_cyan,
- bright_white,
- none.

Note: some terminals allow the user to configure the actual encoding of
those colors. You may thus notice some difference with the expected rendering
of the same colors encoded in the other modes. Use the other color modes if you
want to fully control the actual color rendering.


#### 256-colors mode

For 256-colors mode, colors are expected to be passed as integers in [-1,255]
or the `fg::none` and `bg::none` tags.

In 256-colors mode, if you want to only encode the background color,
you cannot just omit the foreground color,
you have to bass a `fg::none` tag as first argument.

```cpp
log.style(level::info, fg::none, 52); // No color over dark red.
log.style(level::info, fg::none, 52, typo::bold); // No color over bold dark red.
```


#### 16 million colors mode (RGB)

For 16M-colors mode, colors can be encoded as:
- three integer arguments,
- a "web color" hexadecimal triplet string, starting with a leading number sign (e.g. "#0055ff").
- the `fg::none` and `bg::none` tags.

In 16M-colors mode, if you want to only encode the background color,
you cannot just omit the foreground color,
you have to pass a `fg::none` tag as first argument.

```cpp
log.style(level::info, fg::none, 100,0,0); // No color over dark red.
log.style(level::info, fg::none, 100,0,0, typo::bold); // No color over bold dark red.
```


### Value-dependant Format Tags

Some tags can be used to change the style of (part of) the output line,

*depending on its content*.
The `{filehash_fmt}` and `{funchash_fmt}` will introduce a styling sequence
which depends on the current file name, and function name respectively.
The chosen style is chosen at random among the candidate ones,
but will always be the same for each value.

The set of candidate styles can be configured with `clutchlog::filehash_styles`
and `clutchlog::funchash_styles`, which both take a vector of `clutchlog::fmt`
objects as argument:
```cpp
// Either one or the other color for filenames:
log.filehash_styles( { fmt(fg::red),   fmt(fg::yellow) } );
// This would fix the function name style to a single one:
log.funchash_styles( { fmt(typo::bold) } );
// Works with any `fmt` constructor
// (here, shades of blues in 256-colors mode):
log.funchash_styles( { fmt(33), fmt(27), fmt(39), fmt(45) } );
```

The same idea applies to `{depth_fmt}`.
However, if `clutchlog::depth_styles` is configured,
then the styles are chosen *in order*.
That is, a depth of 1 would lead to the first style being chosen.
If the current depth of the stack is larger than the number of configured
styles, then the last one is used.
For example:
```cpp
// Increasingly darker depth level colors (using the 256-colors mode).
log.depth_styles({ fmt(255), fmt(250), fmt(245), fmt(240), fmt(235) });
```

If `clutchlog::depth_styles` is set, the `{depth_marks}` template tag will render
with each mark having each own style corresponding to its depth.
Note: a depth of zero showing no mark, the first style in the list is never applied to marks.


Advanced Usage
==============

More Output Configuration
-------------------------

### Dump Format

The default format of the first line of comment added with the dump macro is
`"# [{name}] {level} in {func} (at depth {depth}) @ {file}:{line}"`.
It can be edited with the `format_comment` method.
If it is set to an empty string, then no comment line is added.
The default can be modified at compile time with `CLUTCHDUMP_DEFAULT_FORMAT`.

By default, the separator between items in the container is a new line.
To change this behaviour, you can change `CLUTCHDUMP_DEFAULT_SEP` or
call the low-level `dump` method.

By default, and if `CLUTCHDUMP_DEFAULT_FORMAT` is not defined,
clutchlog will not put the location-related tags in the message formats
(i.e. `{file}` and `{line}`) when not in Debug builds.


### Stack Depth Mark

The mark used with the `{depth_marks}` tag can be configured with the `clutchlog::depth_mark` method,
and its default with the `CLUTCHLOG_DEFAULT_DEPTH_MARK` macro:
```cpp
log.depth_mark(CLUTCHLOG_DEFAULT_DEPTH_MARK); // Defaults to ">".
```

### Horizontal Filling

The character used with the `{hfill}` tag can be configured wth the `clutchlog::hfill_mark` method,
and its default with the `CLUTCHLOG_DEFAULT_HFILL_MARK` macro:
```cpp
log.hfill_mark(CLUTCHLOG_DEFAULT_HFILL_MARK); // Defaults to '.'.
```

Clutchlog measures the width of the *standard error* channel.
If it is redirected, it may be measured as very large (or very small).
Thus, the `clutchlog::hfill_min` `clutchlog::hfill_max` accessors allow
to set a minimum and a maximum width (in number of characters).
```cpp
log.hfill_max(CLUTCHLOG_DEFAULT_HFILL_MAX); // Defaults to 300.
log.hfill_min(CLUTCHLOG_DEFAULT_HFILL_MIN); // Defaults to 150.
```
Note: clutchlog will use the measured width, unless
it goes out of `[clutchlog::hfill_min,clutchlog::hfill_max]`,
in which case it will be caped to those bounds.


### Stack Depth

By default, clutchlog removes 5 levels of the calls stack, so that your `main`
entrypoint corresponds to a depth of zero.
You can change this behaviour by defining the `CLUTCHLOG_STRIP_CALLS` macro,
or calling `clutchlog::strip_calls`.
```cpp
log.strip_calls(CLUTCHLOG_STRIP_CALLS); // Defaults to 5.
```


Disabled calls
--------------

By default, clutchlog is always enabled if the `NDEBUG` preprocessor variable is not defined
(this variable is set by CMake in build types that differs from `Debug`).

You can however force clutchlog to be enabled in any build type
by setting the `WITH_CLUTCHLOG` preprocessor variable.

When the `NDEBUG` preprocessor variable is set (e.g. in `Release` build),
clutchlog will do its best to allow the compiler to optimize out any calls
for log levels that are under `progress`.

You can change this behavior at compile time by setting the
`CLUTCHLOG_DEFAULT_DEPTH_BUILT_NODEBUG` preprocessor variable
to the desired maximum log level, for example:
```cpp
// Will always allow to log everything even in Release mode.
#define CLUTCHLOG_DEFAULT_DEPTH_BUILT_NODEBUG clutchlog::level::xdebug
```

Note that allowing a log level does not mean that it will actually output something.
If the configured log level at runtime is lower than the log level of the message,
it will still not be printed.

This behavior intend to remove as many conditional statements as possible
when not debugging, without having to use preprocessor guards around
calls to clutchlog, thus saving run time at no readability cost.


Low-level API
-------------

All configuration setters have a getters counterpart, with the same name but taking no parameter,
for example:
```cpp
std::string mark = log.depth_mark();
```

To control more precisely the logging, one can use the low-level `clutchlog::log` method:
```cpp
log.log(clutchlog::level::xdebug, "hello world", "main.cpp", "main", 122);
```
A helper macro can helps to fill in the location with the actual one, as seen by the compiler:
```cpp
log.log(clutchlog::level::xdebug, "hello world", CLUTCHLOC);
```
A similar `dump` method exists:
```cpp
log.dump(clutchlog::level::xdebug, cont.begin(), cont.end(), CLUTCHLOC, "dumped_{n}.dat", "\n");
log.dump(clutchlog::level::xdebug, cont.begin(), cont.end(), "main.cpp", "main", 122, "dumped.dat", "\n\n");
```

You can access the identifier of log levels with `clutchlog::level_of`:
```cpp
log.threshold( log.level_of("XDebug") ); // You have to know the exact string.
```


(De)clutch any function call
----------------------------

The `CLUTHFUNC` macro allows to wrap any function within the current logger.

For instance, this can be useful if you want to (de)clutch calls to `assert`s.
To do that, just declare your own macro:
```cpp
#define ASSERT(...) { CLUTCHFUNC(error, assert, __VA_ARGS__) }
```
Thus, any call like `ASSERT(x > 3);` will be declutchable
with the same configuration than a call to `CLUTCHLOG`.


(De)clutch any code section
---------------------------

The `CLUTCHCODE` macro allows to wrap any code within the current logger.

For instance:
```cpp
CLUTCHCODE(info,
    std::clog << "We are clutched!\n";
);
```


Manually Increase Stack Depth
-----------------------------

You may want to manually increase the stack depth for a given logging call,
for instance to subdivise a single function in sections.
To do so, you can use the `CLUTCHLOGD` macro, which take an additional argument,
in the form of the number of additional (fake) stack depths you want:
```cpp
CLUTCHLOG( debug, "Call"); // Regular macro.
CLUTCHLOGD(debug, "Sub call", 1); // Adds an additional (fake) stack depth.
CLUTCHLOGD(debug, "Sub sub!", 2); // Adds two additional (fake) stack depths.
```
That way, the depth will be rendered to the actual depth, plus the additional
depth delta. Note that the displayed function will stay the same. Any filtering
on the stack depth will take into account the fake depth and not the real one.


Examples
========

Here what you would do to setup clutchlog with the default configuration:
```cpp
    auto& log = clutchlog::logger();
    log.out(std::clog);
    // Location filtering.
    log.depth(std::numeric_limits<size_t>::max());
    log.threshold("Error");
    log.file(".*");
    log.func(".*");
    log.line(".*");
    // Colors of the 3 firsts levels.
    log.style(clutchlog::level::critical, clutchlog::fmt(
            clutchlog::fmt::fg::red,
            clutchlog::fmt::typo::underline);
    log.style(clutchlog::level::error, clutchlog::fmt(
            clutchlog::fmt::fg::red,
            clutchlog::fmt::typo::bold);
    log.style(clutchlog::level::warning, clutchlog::fmt(
            clutchlog::fmt::fg::magenta,
            clutchlog::fmt::typo::bold);
    // Assuming you are on a POSIX system.
    log.format("[{name}] {level_letter}:{depth_marks} {msg} {hfill} {func} @ {file}:{line}\n");
    log.depth_mark(">");
    log.strip_calls(5);
    log.hfill_char('.');
    log.hfill_max(300);
    log.hfill_style(clutchlog::fmt::fg::none);
```

And here are all the functions you may call to log something:
```cpp
    // Basic message.
    CLUTCHLOG(debug, "x = " << x);

    // Any code section.
    CLUTCHCODE(xdebug,
        if(x < 0) std::cerr << "WTF?" << std::endl;
    );

    // Container to a file.
    CLUTCHDUMP(note, my_vector, "my_vector.dat");

    // Container to a numbered file.
    CLUTCHDUMP(note, my_list, "my_list_{n}.dat");

    // Function call.
    CLUTCHFUNC(warning, my_check, x, y); // Calls: my_check(x,y);

    // Declutchable asserts.
    #define ASSERT(...) { CLUTCHFUNC(critical, assert, __VA_ARGS__) }
    ASSERT(x>0);
```

Here what you would do to setup clutchlog with the default configuration
using 16M-colors mode:
```cpp
    auto& log = clutchlog::logger();
    log.out(std::clog);
    // Location filtering.
    log.depth(std::numeric_limits<size_t>::max());
    log.threshold("Error");
    log.file(".*");
    log.func(".*");
    log.line(".*");
    // Colors of the 3 firsts levels.
    log.style(clutchlog::level::critical, clutchlog::fmt(
            "#ff0000",
            clutchlog::fmt::typo::underline);
    log.style(clutchlog::level::error, clutchlog::fmt(
            "#ff0000",
            clutchlog::fmt::typo::bold);
    log.style(clutchlog::level::warning, clutchlog::fmt(
            "#ff00ff",
            clutchlog::fmt::typo::bold);
    // Assuming you are on a POSIX system.
    log.format("[{name}] {level_letter}:{depth_marks} {msg} {hfill} {func} @ {file}:{line}\n");
    log.depth_mark(">");
    log.strip_calls(5);
    log.hfill_char('.');
    log.hfill_max(300);
    log.hfill_style(clutchlog::fmt::fg::none);
```


Limitations
===========

### System-dependent stack depth

Because access to the call stack depth and program name are system-dependent,
the features relying on the depth of the call stack and the display of the program name
are only available for operating systems having the following headers:
`execinfo.h`, `stdlib.h` and `libgen.h` (so far, tested with Linux).

Clutchlog sets the `CLUTCHLOG_HAVE_UNIX_SYSINFO` to 1 if the headers are
available, and to 0 if they are not.
You can make portable code using something like:
```cpp
#if CLUTCHLOG_HAVE_UNIX_SYSINFO == 1
    log.depth( x );
#endif 
```


### System-dependent horizontal fill

Because access to the current terminal width is system-dependent,
the `{hfill}` format tag feature is only available for operating systems having the following headers:
`sys/ioctl.h`, `stdio.h` and `unistd.h` (so far, tested with Linux).

Clutchlog sets the `CLUTCHLOG_HAVE_UNIX_SYSIOCTL` to 1 if the headers are
available, and to 0 if they are not.
You can make portable code using something like:
```cpp
#if CLUTCHLOG_HAVE_UNIX_SYSIOCTL == 1
    log.hfill_mark( '_' );
#endif 
```

If you use unicode characters in your template, the horizontal width will not be
computed properly, resulting in incorrectly right-aligned lines.
Solving this would require the use of third-party libraries, making portability
more difficult.


### Dependencies

Some colors/styles may not be supported by some exotic terminal emulators.

Clutchlog needs `C++-17` with the `filesystem` feature.
You may need to indicate `-std=c++17 -lstdc++fs` to some compilers.


### Variable names within the CLUTCHLOG macro

Calling the `CLUTCHLOG` macro with a message using a variable named `clutchlog__msg` will end in
an error.


### Features

What Clutchlog do not provide at the moment (but may in a near future):

- Super fast log writing.
- Thread safety.

What Clutchlog will most certainly never provide:

- Round-robin log managers.
- Duplicated messages management.
- External output systems (only allow output stream, you can still do the proxy yourself).
- External error handlers (not my job, come on).
- Automatic argument parser (please, use a dedicated lib).
- Signal handling (WTF would you do that, anyway?).


Build and tests
===============

To use clutchlog, just include its header in your code
and either ensure that the `NDEBUG` preprocessor variable is not set,
either define the `WITH_CLUTCHLOG` preprocessor variable.

If you're using CMake (or another modern build system),
it will unset `NDEBUG` —and thus enable clutchlog—
only for the "Debug" build type,
which is usually what you want if you use clutchlog, anyway.

To build and run the tests, just use a classical CMake workflow:
```sh
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug -DWITH_CLUTCHLOG=ON ..
make
ctest
```

There's a script that tests all the build types combinations: `./build_all.sh`.

