Embarking on my journey with ts and currently exploring TypeGraphQL.
I came across something that caught my attention and seems unfamiliar to me:
export declare type ReturnTypeFunc = (returns?: void) => ReturnTypeFuncValue;
How should this type be understood? What is the significance of (returns?: void) in this context?
The ReturnTypeFunc type is utilized within the Query decorator:
export declare function Query(returnTypeFunc: ReturnTypeFunc, options?: AdvancedOptions): MethodDecorator;
This is a common usage of the Query decorator:
@Query(returns => [SampleObject])
To enhance readability, the returns parameter was added: This query returns an array of SampleObject. Without the returns argument in the ReturnTypeFunc type, you would need to write @Query(() => [SampleObject]) instead.
Other decorators that feature an optional void argument include:
@Resolver(of => Recipe) // This resolver is for Recipe. Refer to the ClassTypeResolver.
@Field(type => [Rate]) // This field is of type Rate. Refer to the ClassTypeResolver.
Note:
null (if strictNullChecks is not specified) or undefined can be assigned to a variable of type void.ReturnTypeFunc is not recommended. The purpose of using parameters of type void is primarily for code readability.The function signature provided can be found here, and it utilizes an optional parameter of type void for various reasons.
One possible reason could be to restrict callers from providing an argument in normal scenarios, while allowing internal library code to access undocumented, internal logic that may rely on the functionality of the value.
Here is a somewhat contrived example to illustrate this concept:
function fn (param?: void): void {
if ((param as any) === 'log a special message') {
console.log('Internal behavior matched');
}
};
fn(); // Ok
fn('hello'); // Not ok
/**
* Written as returning void, but actually returns
* something that is used for internal library behavior
*/
function internalFnForInteralThings (): void {
return 'log a special message' as any;
};
fn(internalFnForInteralThings()); // Ok (and logs "Internal behavior matched")
To truly understand the reasoning behind such a signature, one would need to thoroughly analyze the entire codebase of the project exporting the type and assess how it is utilized in each scenario. With this knowledge, one can potentially deduce the rationale behind the author's decision to structure the signature in this manner.
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