Add Kotlin-style logging API with lambda support

Introduced new Kotlin-style logging methods using lambda expressions, which are evaluated only if the respective log level is enabled. Updated README.md and tests to demonstrate the usage of these new methods.

README.md

@@ -31,13 +31,31 @@ Each appender may also have its own `Channel`, which is especially useful
 for cases requiring batching—such as sending batched log or trace events over the network or
 appending them to a file.
 
+## API
+
+```kotlin
+log.info("this is test log")
+log.info("this is test with 1 arg: {}", "hello")
+log.error(e.message, e)
+```
+
+We also support a more kotlin style API:
+
+```kotlin
+log.debug { "ignore" }
+log.debug { "ignore + ${5}" } // Will be evaluated only if DEBUG logs are enabled.
+log.error { e.message }
+log.error(e) { e.message } // e: Throwable
+```
+
 ## Examples
 
 ```kotlin
 // Create a Logger.
 private val log: Logger = Logger.of(this::class)
 
 log.debug("ignore")
+log.debug { "ignore + ${5}" } // Will be evaluated only if DEBUG logs are enabled.
 log.info("this is a test")
 
 // Support for mute/unmute each logger programmatically.

log4k/src/commonMain/kotlin/io/github/smyrgeorge/log4k/Logger.kt

@@ -50,13 +50,18 @@ abstract class Logger {
         levelBeforeMute = level
     }
 
+    fun trace(f: () -> String): Unit = if (Level.TRACE.shouldLog()) trace(f()) else Unit
     fun trace(msg: String, vararg args: Any?): Unit = log(Level.TRACE, msg, args)
+    fun debug(f: () -> String): Unit = if (Level.DEBUG.shouldLog()) debug(f()) else Unit
     fun debug(msg: String, vararg args: Any?): Unit = log(Level.DEBUG, msg, args)
+    fun info(f: () -> String): Unit = if (Level.INFO.shouldLog()) info(f()) else Unit
     fun info(msg: String, vararg args: Any?): Unit = log(Level.INFO, msg, args)
+    fun warn(f: () -> String): Unit = if (Level.WARN.shouldLog()) warn(f()) else Unit
     fun warn(msg: String, vararg args: Any?): Unit = log(Level.WARN, msg, args)
+    fun error(f: () -> String?): Unit = if (Level.ERROR.shouldLog()) error(f()) else Unit
     fun error(msg: String?, vararg args: Any?): Unit = log(Level.ERROR, msg ?: "", args)
-    fun error(msg: String?, throwable: Throwable, vararg args: Any?): Unit =
-        log(Level.ERROR, msg ?: "", throwable, args)
+    fun error(t: Throwable, f: () -> String?): Unit = if (Level.ERROR.shouldLog()) error(f(), t) else Unit
+    fun error(msg: String?, t: Throwable, vararg args: Any?): Unit = log(Level.ERROR, msg ?: "", t, args)
 
     companion object {
         fun of(name: String): Logger = RootLogger.factory.getLogger(name)

log4k/src/commonTest/kotlin/io/github/smyrgeorge/log4k/MainTests.kt

@@ -19,6 +19,7 @@ class MainTests {
     @Test
     fun test() {
         log.debug("ignore")
+        log.debug { "ignore + ${5}" } // Will be evaluated only if DEBUG logs are enabled.
         log.info("this is a test")
         RootLogger.loggers.mute("io.github.smyrgeorge.log4k.MainTests")
         log.info("this is a test with 1 arg: {}", "hello")
@@ -29,7 +30,9 @@ class MainTests {
             error("An error occurred!")
         } catch (e: Exception) {
             log.error(e.message)
+            log.error { e.message }
             log.error(e.message, e)
+            log.error(e) { e.message }
         }
 
         runBlocking {