proposal: reflect: add TypeByName to create a type giving its fully-qualified name

[andig]

Proposal Details

Consider adding a function to the reflect package for creating a type by it's name:

// `TypeByName` creates a Type given its name.
// It panics if the result type is not reachable.
func TypeByName(name string) Type

This can e.g. be useful with generated code where the go generate directive contains information about the required types. Having TypeByName allows the generate implementation to reason about the types without having to hard-code them.

Example:

typ := reflect.TypeByName("api.Meter")
val := reflect.New(typ)
for i := range val.NumMethod() {
    m := val.Method(i)
}

To work around

It panics if the result type is not reachable.

generate (or any other package using this function) would still need to (_) import the type's packages.

Note: this proposal is equivalent to the older #21754 but adds a use case.

[gabyhelp]

Related Issues and Documentation

• proposal: reflect: add GetTypeByName function #21754 (closed)
• reflect: NamedOf #16522
• reflect: add TypeFor #60088 (closed)

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[robpike]

Duplicate of closed #21754. The new use case does not address the dead code elimination problem of the first proposal.

[andig]

This allows the linker to aggressively remove dead code, making binaries smaller. Otherwise, when you import a package, all of the code in that package would have to be included in the final binary, because the linker does not know what will be requested at run time.

I do feel that the panic adequately explains that linker can proceed as needed. This would only give access to the types that already are included. But maybe this is too clumsy or awkward?

[seankhliao]

Duplicate of #21754