SLF4D Documentation

# Using SLF4D

It's easy to write log messages with SLF4D. All you need to do is import slf4d;, and call the log message of your choice.

import slf4d;

void doSomething() {
    try {
        info("Doing something risky...");
        throw new Exception("Yikes");
    } catch (Exception e) {
        error("Uh oh, an error occurred!", e);
    }
}

# Logging Levels

SLF4D defines a Level struct with a name and an integer value that depicts its severity (with higher values being more severe). While you can create your own custom logging levels if you need, SLF4D provides a standard set of logging levels via the Levels enum.

Level Value Meaning
Levels.TRACE 10 The lowest severity log level defined by SLF4D, usually for fine-grained debugging of individual statements and control flow.
Levels.DEBUG 20 A low severity log level used for extra information that's only useful when debugging a program's behavior.
Levels.INFO 30 A medium severity log level used for reporting information during standard, nominal program operation.
Levels.WARN 40 A higher severity log level for reporting anomalous but non-fatal issues that arise at runtime.
Levels.ERROR 50 A severe log level for program errors that indicate a fatal bug that leads to program failure or inconsistent state.

# The Logger

All log messages are generated using a Logger struct. You can obtain a logger via the getLogger() function. Each logger has a name, which defaults to the name of the D module from which getLogger() was called.

Logger logger = getLogger();
Logger namedLogger = getLogger("custom-name");

Note: Unless you want a logger with a custom name, it's easier to just use the logging functions without specifying a Logger.

# Logging Functions

SLF4D defines the following 3 types of logging functions:

  1. Basic message logs - Write a log message string, at a specified log level. You can optionally include an Exception.
  2. Exception logs - Write a log message at a specified log level, from an Exception that was thrown.
  3. Formatted logs - Write a formatted log message at a specified log level, using a series of format arguments. This ultimately gets formatted by std.format : format.

These are illustrated below:

// 1.
log(Levels.DEBUG, "This is a basic log message.");
log(Levels.TRACE, "Another basic message", new Exception("With exception"));
// 2.
log(Levels.ERROR, new Exception("An exception log message."));
// 3.
logF!"This is a formatted log message: %d"(Levels.INFO, 42);

Because SLF4D defines a set of standard logging levels, it also includes a variant of each of the above functions, for each logging level. The snippet below shows some of these functions, but for a complete list, check the slf4d.log_functions module.

info("This is an info message.");
traceF!"Calling function with args: %s"(args);
debug_("This is a debug message.");
try {
    doSomethingRisky();
} catch (Exception e) {
    error(e);
}

Note: Because debug is a D language keyword, instead of writing debug("msg");, you should write log.debug_("msg");.

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