Constraint Usage

This page informs on how to use Iron's constraints.

Basic usage

You can attach a constraint to:

• Variables
• Methods (Return type)
• Parameters

using the type Constrained[A, B] or its alias ==>[A, B]:

inline def log(x: Double ==> Greater[0d]): Double = Math.log(x)

You can also use type aliases:

type >[A, V] = A ==> Greater[V]

inline def log(x: Double > 0d): Double = Math.log(x)

Note: You need to have a suitable constraint behaviour in the implicit scope.

Compile time evaluation

A constraint is evaluated at compile time if the value and the behaviour is fully inline. Otherwise, the compiler will inline as much as possible the constraint then evaluate at runtime. Runtime evaluation is disabled by default but can be useful for dynamic values.

Runtime fallback

The fallback behaviour can be configured using the -Diron.fallback argument:

• error (default): Throw a compile time error
• warn: Warn, then fallback to runtime
• allow: Silently fallback to runtime