Add loggers that take functions as input

.gitignore

@@ -1,2 +1,4 @@
 logrus
 vendor
+
+.idea/

example_function_test.go

@@ -0,0 +1,26 @@
+package logrus_test
+
+import (
+	"fmt"
+	log "github.com/sirupsen/logrus"
+	"testing"
+)
+
+func TestLogger_LogFn(t *testing.T) {
+	log.SetFormatter(&log.JSONFormatter{})
+	log.SetLevel(log.WarnLevel)
+
+	log.InfoFn(func() []interface{} {
+		fmt.Println("This is never run")
+		return []interface{} {
+			"Hello",
+		}
+	})
+
+	log.ErrorFn(func() []interface{} {
+		fmt.Println("This runs")
+		return []interface{} {
+			"Oopsi",
+		}
+	})
+}

exported.go

@@ -134,6 +134,51 @@ func Fatal(args ...interface{}) {
 	std.Fatal(args...)
 }
 
+// TraceFn logs a message from a func at level Trace on the standard logger.
+func TraceFn(fn LogFunction) {
+	std.TraceFn(fn)
+}
+
+// DebugFn logs a message from a func at level Debug on the standard logger.
+func DebugFn(fn LogFunction) {
+	std.DebugFn(fn)
+}
+
+// PrintFn logs a message from a func at level Info on the standard logger.
+func PrintFn(fn LogFunction) {
+	std.PrintFn(fn)
+}
+
+// InfoFn logs a message from a func at level Info on the standard logger.
+func InfoFn(fn LogFunction) {
+	std.InfoFn(fn)
+}
+
+// WarnFn logs a message from a func at level Warn on the standard logger.
+func WarnFn(fn LogFunction) {
+	std.WarnFn(fn)
+}
+
+// WarningFn logs a message from a func at level Warn on the standard logger.
+func WarningFn(fn LogFunction) {
+	std.WarningFn(fn)
+}
+
+// ErrorFn logs a message from a func at level Error on the standard logger.
+func ErrorFn(fn LogFunction) {
+	std.ErrorFn(fn)
+}
+
+// PanicFn logs a message from a func at level Panic on the standard logger.
+func PanicFn(fn LogFunction) {
+	std.PanicFn(fn)
+}
+
+// FatalFn logs a message from a func at level Fatal on the standard logger then the process will exit with status set to 1.
+func FatalFn(fn LogFunction) {
+	std.FatalFn(fn)
+}
+
 // Tracef logs a message at level Trace on the standard logger.
 func Tracef(format string, args ...interface{}) {
 	std.Tracef(format, args...)

logger.go

@@ -9,6 +9,11 @@ import (
 	"time"
 )
 
+// LogFunction For big messages, it can be more efficient to pass a function
+// and only call it if the log level is actually enables rather than
+// generating the log message and then checking if the level is enabled
+type LogFunction func()[]interface{}
+
 type Logger struct {
 	// The logs are `io.Copy`'d to this in a mutex. It's common to set this to a
 	// file, or leave it default which is `os.Stderr`. You can also set this to
@@ -195,6 +200,14 @@ func (logger *Logger) Log(level Level, args ...interface{}) {
 	}
 }
 
+func (logger *Logger) LogFn(level Level, fn LogFunction) {
+	if logger.IsLevelEnabled(level) {
+		entry := logger.newEntry()
+		entry.Log(level, fn()...)
+		logger.releaseEntry(entry)
+	}
+}
+
 func (logger *Logger) Trace(args ...interface{}) {
 	logger.Log(TraceLevel, args...)
 }
@@ -234,6 +247,45 @@ func (logger *Logger) Panic(args ...interface{}) {
 	logger.Log(PanicLevel, args...)
 }
 
+func (logger *Logger) TraceFn(fn LogFunction) {
+	logger.LogFn(TraceLevel, fn)
+}
+
+func (logger *Logger) DebugFn(fn LogFunction) {
+	logger.LogFn(DebugLevel, fn)
+}
+
+func (logger *Logger) InfoFn(fn LogFunction) {
+	logger.LogFn(InfoLevel, fn)
+}
+
+func (logger *Logger) PrintFn(fn LogFunction) {
+	entry := logger.newEntry()
+	entry.Print(fn()...)
+	logger.releaseEntry(entry)
+}
+
+func (logger *Logger) WarnFn(fn LogFunction) {
+	logger.LogFn(WarnLevel, fn)
+}
+
+func (logger *Logger) WarningFn(fn LogFunction) {
+	logger.WarnFn(fn)
+}
+
+func (logger *Logger) ErrorFn(fn LogFunction) {
+	logger.LogFn(ErrorLevel, fn)
+}
+
+func (logger *Logger) FatalFn(fn LogFunction) {
+	logger.LogFn(FatalLevel, fn)
+	logger.Exit(1)
+}
+
+func (logger *Logger) PanicFn(fn LogFunction) {
+	logger.LogFn(PanicLevel, fn)
+}
+
 func (logger *Logger) Logln(level Level, args ...interface{}) {
 	if logger.IsLevelEnabled(level) {
 		entry := logger.newEntry()