HttpParams fromObject should accept ReadonlyArray<string>

[jinder]

🚀 feature request

Relevant Package

@angular/common/http

Description

The type definition for HttpParamsOptions fromObject property only accepts string and string[]. If using immutable types, such as ReadonlyArray, you must create a new array unnecessarily to satisfy the type.

Describe the solution you'd like

Please change the type to the following (which is backwards compatible):

    fromObject?: {
        [param: string]: string | string[] | ReadonlyArray<string>;
    };

[alan-mroczek]

Hi @jinder. How about without second array, just by casting types:

fromObject: { yourParamName: ['example', 'example2'] as string[] }

I can create PR with that change, because it shouldn't be that hard to implement, but I'm not sure if it's needed.

[jinder]

@alan-mroczek I think it's poor practice to cast a immutable type to a mutable one (and preferable to slice it if need be).

Angular's API surface should really use immutable types where possible (i.e. where it is not mutating them), as they are subset of the mutable version.

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