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Comparative Constraints in Go Generics: Understanding Order Operator Limitations

In Go generics, comparing numerical values can be achieved using either a custom type constraint or the built-in comparable constraint. However, using the comparable constraint with order operators like > may raise an error.

The comparable Constraint

The comparable constraint is used for types that support equality operators == and !=. It is also applicable to types used as map keys, including arrays and structs with comparable fields. However, note that it does not support order operators (, >=).

Order Operators and constraints.Ordered

Order operators are only applicable to types that implement the constraints.Ordered interface. This interface defines a partial ordering for the types it represents. However, in Go versions 1.18 to 1.20, the constraints.Ordered interface is only available in the experimental golang.org/x/exp package.

Go 1.21 Solution

In Go 1.21, the cmp package introduces the Ordered constraint and two generic functions, Less and Compare, that facilitate comparisons for ordered types.

Workaround for Go 1.18 to 1.20

In Go versions 1.18 to 1.20, you can use the golang.org/x/exp package to access the constraints.Ordered interface. Alternatively, you can implement your own custom type that satisfies the constraints.Ordered interface and use that in your generic functions.

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