What Is the comparable Constraint in Go

The comparable constraint is a predeclared interface that restricts generic type parameters to types that support equality comparison using == or !=. It includes booleans, numbers, strings, pointers, channels, and structs composed of comparable fields, but excludes slices, maps, and functions. You use it in generic function or type definitions to ensure the type parameter can be compared.

func Contains[T comparable](slice []T, item T) bool {
	for _, v := range slice {
		if v == item {
			return true
		}
	}
	return false
}

The comparable constraint acts like a rulebook for generic code, allowing you to use types that can be checked for equality. It ensures that any type you pass into your function can be compared with == or !=, preventing errors with types like slices or maps that cannot be compared directly. Think of it as a filter that only lets in data types that can be safely matched against each other.