Expose isTypeReference function in public API

Search Terms

isTypeReference

Suggestion

The public compiler API exposes a getTypeArguments method on the type checker:

https://github.com/microsoft/TypeScript/blob/cc7cb9eadb10a56687513d4fc3a67d5210b387bb/lib/typescript.d.ts#L2107

But provides no way to check if a type is a TypeReference. Users of the TS compiler API have to roll their own, which is error-prone. I suggest that if TypeReference is exposed in the public API, there should be a way to assert whether a type is a TypeReference.

Use Cases

See above

Examples

Currently, public uses of getTypeArguments must do something like this to assert that a type is a TypeReference:

function isTypeReference(ty: ts.Type): ty is ts.TypeReference {
    return 'typeArguments' in ty;
}

const ty = getType();
if (isTypeReference(ty)) {
    getChecker().getTypeArguments(ty);
}

With an exposed type guards, this becomes

const ty = getType();
if (ts.isTypeReference(ty)) {
    getChecker().getTypeArguments(ty);
}

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

まず、公開されている getTypeArguments メソッドとパブリックな TypeReference API の周辺にある lib/typescript.d.ts を調べます。完成した API が ts.isTypeReference を公開していること、および例でそれを使って getTypeArguments の呼び出しをガードできることを確認します。