$Call with arguments has confusing documentation

[kumar303]

Description

The documentation for $Call is unclear:

// Common use-case
const add = (amount: number) => ({ type: 'ADD' as 'ADD', payload: amount });
type AddAction = $Call<typeof returnOfIncrement>; // { type: 'ADD'; payload: number }

What is returnOfIncrement and where does it come from?

I read #21 but I still don't understand. Thanks for your help.

Steps to Reproduce

1. Try to port Flow to TS using $Call where $Call originally was given two arguments
2. Read the docs to figure out how to convert this code to TS

Expected behavior

The docs should provide a more clear example of how to convert old Flow style usage of $Call with arguments.

Suggested solution(s)

Provide an example of working TypeScript code in the docs

Project Dependencies

• Utility-Types Version: 3.10.0
• TypeScript Version: 3.9.7

tsconfig.json

{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    /* Basic Options */
    // "incremental": true,                   /* Enable incremental compilation */
    "target": "ES2015",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
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    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
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    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
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  }
}

Environment (optional)

• Browser and Version: XXX
• OS: XXX
• Node Version: XXX
• Package Manager and Version: XXX

[kumar303]

Oh! Is this what it should be?

// Common use-case
const add = (amount: number) => ({ type: 'ADD' as 'ADD', payload: amount });
type AddAction = $Call<typeof add>; // { type: 'ADD'; payload: number }

[piotrwitek]

Oh! Is this what it should be?

Yes, it's a typo in docs, PR is welcomed!

Regarding the OP issue, it's impossible to implement the same behavior using TS as it's used in Flow at the moment, so we are using a simpler alternative.

Maybe the solution here is to change the name/description so it's less confusing. Feel free to suggest something better and open a PR. I'll be happy to help and the community will benefit from it.

[kumar303]

Oh! Is this what it should be?

Yes, it's a typo in docs, PR is welcomed!

Ah, great. I just edited on the GitHub site: #154

Regarding the OP issue, it's impossible to implement the same behavior using TS as it's used in Flow at the moment, so we are using a simpler alternative.

Maybe the solution here is to change the name/description so it's less confusing. Feel free to suggest something better and open a PR. I'll be happy to help and the community will benefit from it.

Hmm, I'm not sure. I guess it's fine. I was converting from Flow so I ended up just going with the built-in ReturnType in most places instead of $Call because it handled union types better. I could link to ReturnType in the docs if you'd like.

You may be aware already but flow-to-ts automatically converts to $Call from utility-types.

[piotrwitek]

Thanks for the typo fix!

I  think adding the comment and linking to build-in ReturnType would be great for inexperienced users 👍 Basically they should work the same.

[kumar303]

I think adding the comment and linking to build-in ReturnType would be great for inexperienced users 👍 Basically they should work the same.

Sure. I proposed this #155

[piotrwitek]

I think this can be closed now.