How Can I Safely Use Order Operators (, =) with Go Generics?

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Go Generics: Order Operators with Comparable Constraints

In Go 1.18, generics allow for tailored constraints to enforce type compatibility. However, when attempting to use the '>' operator with the 'comparable' constraint, errors may arise.

The 'comparable' Constraint

The 'comparable' constraint verifies that a type supports equality operators ('==' and '!='). It encompasses types eligible as map keys, including arrays and structs with comparable fields. Notably, interfaces are excluded as they may cause runtime panics during comparison.

Ordered vs. Comparable

While the Go specifications mention order operators under the term "comparison operators," they differentiate between equivalence ('==' and '!=') and ordering operators ('<', '>', '<=', '>='). Ordering is constrained to types that are 'ordered.'

Go Versions and Solutions

Go 1.21

• Introduce 'cmp.Ordered' from the standard library.

Go 1.18 to 1.20

• Utilize 'constraints.Ordered' from the experimental 'golang.org/x/exp' package. This constraint supports order operators and includes integers, floats, and strings.

Example:

import "golang.org/x/exp/constraints"

func getBiggerNumber[T constraints.Ordered](t1, t2 T) T {
    if t1 > t2 {
        return t1
    }
    return t2
}

By choosing the appropriate constraint, you ensure type compatibility and correct comparison behavior in your generic functions.

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