microsoft / microsoft/TypeScript
Infer method name for parameter decorator
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描述
TypeScript Version: 3.3.3
Tried with @next (3.4.0-dev.201xxxxx) ? NO
Search Terms: type:issues infer method name parameter decorator
Code
declare function Method():
{
(t: any, m: 'method'): void;
}
declare function Parameter():
{
(t: any, m: 'method', i: number): void;
}
class Play
{
@Method() // err
public another_method ( @Parameter() /* NO ERROR */ test: number ): void
{
throw new Error('Not yet implemented');
}
@Method()
public method ( @Parameter() test: number ): void
{
throw new Error('Not yet implemented');
}
}
Expected behavior: @Parameter() should error just as @Method() when applied to another_method() because the m parameter is typed "method" (which should reduced the set of method). i.e method name should be enforced.
Actual behavior: No error
Playground Link: https://typescript-play.js.org
Use case :
I crafted a type that filters method names with the nth parameters iff that parameters is of the given type T.
See KeysToTypedNthParameter definition here
let hash = {
a( _0: string, _1: string ) {},
b( _0: string, _1: number ) {},
c( _0: number, _1: number ) {},
d( _0: number, _1: string ) {},
}
let string_0: KeysToTypedNthParameter<0, string, typeof hash>; // "a" | "b"
let string_1: KeysToTypedNthParameter<1, string, typeof hash>; // "a" | "d"
let number_0: KeysToTypedNthParameter<0, number, typeof hash>; // "c" | "d"
let number_1: KeysToTypedNthParameter<1, number, typeof hash>; // "c" | "d"
Later, I used that type to infer method name for my parameter decorator - @Inject - in the excerpt below, I marked the ONLY line that should error and why (but both lines actually error)
class Test
{
public blatantly!: boolean;
}
class Play
{
public method(
@Inject({ type: Test })
@Inject({ type: Number }) // err (construtor mismatch instance type)
test: Test,
): void
{
throw new Error( 'Not yet implemented' );
}
}
Play;
Here is @Inject decorator definition and complete code -
const Inject: InjectLike = void 0 as unknown as InjectLike;
interface InjectLike
{
<
C extends ConstructorLike,
>
({}: { type: C }): {
<
// FIXME : not enough to infer the method name - see ./__playground.ts#
M extends ( T extends ConstructorLike ? never : KeysToTypedNthParameter<I, InstanceType<C>, T> ),
I extends number,
T,
>
( target: T, member: M, index: I ): void;
};
}
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调研方向
首先在链接的 TypeScript Playground 中复现 decorator 示例,包括 InjectLike 定义及其对 __playground.ts 的引用。跟踪泛型方法名、参数索引和目标类型的推断方式;完成的标准是:@Parameter() 在 another_method() 上报错,而有效的 @Inject 用法被接受,并且标记的构造函数不匹配被拒绝。
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