Swift中使用Promise实现并行任务：Promises.zip与Promises.all的选择

Hey there! Let's clear up the confusion between Promises.zip and Promises.all, then figure out which one fits your use case perfectly.

Let's break down their core behaviors:

Promises.all #

• Accepts an array of Promises as input.
• Only resolves when every input Promise succeeds, returning an array of results that matches the order of the original Promises.
• If any single Promise rejects, it will immediately reject the entire operation—no waiting for the other Promises to finish.

Promises.zip #

• Behavior can vary a bit by library, but the main idea is to pair results from multiple Promises (or sequences of Promises).
• For two individual Promises (like your two tasks), it will resolve to a tuple/array (e.g., [resultA, resultB]) once both are done.
• Some implementations will wait for all Promises to settle (whether they resolve or reject) before moving forward, unlike all which bails early on a rejection. Always double-check your library's docs for specifics!
• It's especially handy when working with parallel sequences (like zipping results from two lists of Promises), but works just as well for standalone tasks.

Your goal is to run two tasks in parallel, wait for both to finish, then use both results for a third task. Here's how to decide:

• Go with Promises.all if: You need both tasks to succeed to proceed, and you want the operation to fail right away if either task fails. This is the standard choice for simple parallel workflows where all results are required.
  Example code snippet:

  // Run tasks in parallel
  const [task1Result, task2Result] = await Promise.all([runTask1(), runTask2()]);
  // Use both results for the third task
  await runThirdTask(task1Result, task2Result);
  

• Consider Promises.zip if: You need to handle cases where one task might fail but still want to access the result of the successful one, or if you're working with multiple sequences of Promises. If your library's zip behaves identically to all for single Promises, it's mostly a stylistic choice—both will get the job done.

A quick note: Native JavaScript Promises don't include Promise.zip out of the box; this is usually a method from libraries like Bluebird. For vanilla JS environments, Promise.all is the universally recognized option. For library-specific implementations, zip adds flexibility when dealing with paired sequences.

内容的提问来源于stack exchange，提问作者Jaythaking