Go generics compile errors: 'T (type X) does not satisfy comparable', 'X does not satisfy constraint', 'cannot use generic function without instantiation': how do I fix constraint errors?

Cause: Every Go type parameter has a constraint, which is an interface that defines the set of allowed type arguments. A type argument satisfies a constraint if it is in that constraint's type set. The compiler rejects instantiations where it is not. Frequent cases: using a slice, map or func type as a map key or with == under the comparable constraint (the spec lists []byte as not satisfying comparable); passing a named type such as type MyInt int to a constraint written as int (it needs ~int to include types with that underlying type); calling < on a type parameter constrained by any; and using a pointer-receiver method set that the value type does not have. Fix: 1. Read which type and which constraint the error names, then compare against the constraint's definition. 2. Choose the right constraint: comparable for ==, a union like ~int | ~float64 | ~string for ordering, or the standard library's cmp.Ordered (documented in package cmp) for < and >. Interfaces with methods work too. 3. Add the tilde (~int) to accept defined types whose underlying type is int. 4. For uncomparable types, change the function to take a comparison or key function parameter, or use a comparable representation such as a string key or struct of comparable fields. 5. If inference fails, supply type arguments explicitly: F[int](x). 6. Remember that interface types such as any can satisfy comparable, but comparing such values can panic at run time if the dynamic types are not comparable. Verify: go build ./... and go vet ./... succeed; add a test instantiating the function with each type you intend to support. Sources: https://go.dev/ref/spec https://go.dev/doc/faq https://go.dev/blog/intro-generics