How to Use regexp.MustCompile vs regexp.Compile in Go

Strings
2026-04-17T12:05:42+00:00
Use regexp.MustCompile for static, pre-validated patterns and regexp.Compile for dynamic patterns requiring error handling.

Use regexp.MustCompile for patterns defined at package initialization or used repeatedly, as it panics on invalid syntax and caches the compiled result. Use regexp.Compile when the pattern is dynamic, user-provided, or defined inside a function where you need to handle compilation errors gracefully.

// Compile once at package level for static patterns
var emailPattern = regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)

// Compile inside a function for dynamic patterns
func validateUserInput(pattern string) (*regexp.Regexp, error) {
    return regexp.Compile(pattern)
}