Porting python's 'with' construct to TypeScript












1












$begingroup$


Now that async generators are available in the platforms I care about, I figured I'd try porting Python's ingenious with construct to JS as a utility. My first stab looks like this:



type Index = string | symbol | number;
function isIndex(obj: any): obj is Index {
return (
typeof obj === 'string' ||
typeof obj === 'symbol' ||
typeof obj === 'number'
);
}
type Disposable<TDisposerKey extends Index> = {
[k in TDisposerKey]: DisposerMethod
};
type DisposerMethod = () => void | Promise<void>;
type DisposerCallback<TDisposable> = (res: TDisposable) => void | Promise<void>;

function using<
TDisposerKey extends Index,
TDisposable extends Disposable<TDisposerKey>
>(resource: TDisposable, key: TDisposerKey): AsyncIterable<TDisposable>;
function using<TDisposable>(
resource: TDisposable,
disposer: DisposerCallback<TDisposable>
): AsyncIterable<TDisposable>;
async function* using<
TDisposerKey extends Index,
TDisposable extends Disposable<TDisposerKey>
>(
resource: TDisposable,
keyOrDisposer: TDisposerKey | DisposerCallback<TDisposable>
): AsyncIterable<TDisposable> {
try {
yield resource;
} finally {
if (typeof keyOrDisposer === 'function') {
await keyOrDisposer(resource);
} else if (isIndex(keyOrDisposer)) {
await resource[keyOrDisposer]();
}
}
}

async function main(): Promise<any> {
for await (const db of using(new PouchDB('zz-data\foo'), 'close')) {
console.dir(await db.info());
return await db.get('qwertyuiop');
}
}


Does anything jump out at anybody? A for..await..of loop with only one iteration is odd, but it's the only way to handle this lexically, and it saves me having to juggle types for a callback-based alternative which was fiddly to make generic. The overloads are also a mouthful, but that's TS for you.










share|improve this question











$endgroup$

















    1












    $begingroup$


    Now that async generators are available in the platforms I care about, I figured I'd try porting Python's ingenious with construct to JS as a utility. My first stab looks like this:



    type Index = string | symbol | number;
    function isIndex(obj: any): obj is Index {
    return (
    typeof obj === 'string' ||
    typeof obj === 'symbol' ||
    typeof obj === 'number'
    );
    }
    type Disposable<TDisposerKey extends Index> = {
    [k in TDisposerKey]: DisposerMethod
    };
    type DisposerMethod = () => void | Promise<void>;
    type DisposerCallback<TDisposable> = (res: TDisposable) => void | Promise<void>;

    function using<
    TDisposerKey extends Index,
    TDisposable extends Disposable<TDisposerKey>
    >(resource: TDisposable, key: TDisposerKey): AsyncIterable<TDisposable>;
    function using<TDisposable>(
    resource: TDisposable,
    disposer: DisposerCallback<TDisposable>
    ): AsyncIterable<TDisposable>;
    async function* using<
    TDisposerKey extends Index,
    TDisposable extends Disposable<TDisposerKey>
    >(
    resource: TDisposable,
    keyOrDisposer: TDisposerKey | DisposerCallback<TDisposable>
    ): AsyncIterable<TDisposable> {
    try {
    yield resource;
    } finally {
    if (typeof keyOrDisposer === 'function') {
    await keyOrDisposer(resource);
    } else if (isIndex(keyOrDisposer)) {
    await resource[keyOrDisposer]();
    }
    }
    }

    async function main(): Promise<any> {
    for await (const db of using(new PouchDB('zz-data\foo'), 'close')) {
    console.dir(await db.info());
    return await db.get('qwertyuiop');
    }
    }


    Does anything jump out at anybody? A for..await..of loop with only one iteration is odd, but it's the only way to handle this lexically, and it saves me having to juggle types for a callback-based alternative which was fiddly to make generic. The overloads are also a mouthful, but that's TS for you.










    share|improve this question











    $endgroup$















      1












      1








      1


      1



      $begingroup$


      Now that async generators are available in the platforms I care about, I figured I'd try porting Python's ingenious with construct to JS as a utility. My first stab looks like this:



      type Index = string | symbol | number;
      function isIndex(obj: any): obj is Index {
      return (
      typeof obj === 'string' ||
      typeof obj === 'symbol' ||
      typeof obj === 'number'
      );
      }
      type Disposable<TDisposerKey extends Index> = {
      [k in TDisposerKey]: DisposerMethod
      };
      type DisposerMethod = () => void | Promise<void>;
      type DisposerCallback<TDisposable> = (res: TDisposable) => void | Promise<void>;

      function using<
      TDisposerKey extends Index,
      TDisposable extends Disposable<TDisposerKey>
      >(resource: TDisposable, key: TDisposerKey): AsyncIterable<TDisposable>;
      function using<TDisposable>(
      resource: TDisposable,
      disposer: DisposerCallback<TDisposable>
      ): AsyncIterable<TDisposable>;
      async function* using<
      TDisposerKey extends Index,
      TDisposable extends Disposable<TDisposerKey>
      >(
      resource: TDisposable,
      keyOrDisposer: TDisposerKey | DisposerCallback<TDisposable>
      ): AsyncIterable<TDisposable> {
      try {
      yield resource;
      } finally {
      if (typeof keyOrDisposer === 'function') {
      await keyOrDisposer(resource);
      } else if (isIndex(keyOrDisposer)) {
      await resource[keyOrDisposer]();
      }
      }
      }

      async function main(): Promise<any> {
      for await (const db of using(new PouchDB('zz-data\foo'), 'close')) {
      console.dir(await db.info());
      return await db.get('qwertyuiop');
      }
      }


      Does anything jump out at anybody? A for..await..of loop with only one iteration is odd, but it's the only way to handle this lexically, and it saves me having to juggle types for a callback-based alternative which was fiddly to make generic. The overloads are also a mouthful, but that's TS for you.










      share|improve this question











      $endgroup$




      Now that async generators are available in the platforms I care about, I figured I'd try porting Python's ingenious with construct to JS as a utility. My first stab looks like this:



      type Index = string | symbol | number;
      function isIndex(obj: any): obj is Index {
      return (
      typeof obj === 'string' ||
      typeof obj === 'symbol' ||
      typeof obj === 'number'
      );
      }
      type Disposable<TDisposerKey extends Index> = {
      [k in TDisposerKey]: DisposerMethod
      };
      type DisposerMethod = () => void | Promise<void>;
      type DisposerCallback<TDisposable> = (res: TDisposable) => void | Promise<void>;

      function using<
      TDisposerKey extends Index,
      TDisposable extends Disposable<TDisposerKey>
      >(resource: TDisposable, key: TDisposerKey): AsyncIterable<TDisposable>;
      function using<TDisposable>(
      resource: TDisposable,
      disposer: DisposerCallback<TDisposable>
      ): AsyncIterable<TDisposable>;
      async function* using<
      TDisposerKey extends Index,
      TDisposable extends Disposable<TDisposerKey>
      >(
      resource: TDisposable,
      keyOrDisposer: TDisposerKey | DisposerCallback<TDisposable>
      ): AsyncIterable<TDisposable> {
      try {
      yield resource;
      } finally {
      if (typeof keyOrDisposer === 'function') {
      await keyOrDisposer(resource);
      } else if (isIndex(keyOrDisposer)) {
      await resource[keyOrDisposer]();
      }
      }
      }

      async function main(): Promise<any> {
      for await (const db of using(new PouchDB('zz-data\foo'), 'close')) {
      console.dir(await db.info());
      return await db.get('qwertyuiop');
      }
      }


      Does anything jump out at anybody? A for..await..of loop with only one iteration is odd, but it's the only way to handle this lexically, and it saves me having to juggle types for a callback-based alternative which was fiddly to make generic. The overloads are also a mouthful, but that's TS for you.







      async-await typescript






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      share|improve this question




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      edited 3 mins ago









      200_success

      129k15153415




      129k15153415










      asked 10 hours ago









      millimoosemillimoose

      29527




      29527






















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