![]() ![]() Going back to the starting example, we can now call merge(bObj, aObj), and the type system will allow us to access value.a, but it will yell at us if we try to access value.b. So that’s it for the function definition. ![]() Otherwise, the the value’s type is just determined by T.ĭefined is just a helper to keep unwanted undefineds out of our end result. if a property is optional, then undefined extends T will be true, so the output value could come from T or U. This uses the newly added extends keyword to pick between values being defined by either T or U. There’s currently an issue for it.Ĭonst merge = (t: T, u: U) => Object.assign( Unfortunately, at the time of this writing, TypeScript can’t handle this you’ll get a Spread types may only be created from object types error. Essentially, I want a function that has a signature like this:Ĭonst merge = (t: T, u: U) => // merge t and uĪ first attempt could look something like this: By “merge,” I mean that I want to replicate the functionality of Object.assign with a finite number of arguments. The task I want to accomplish is to create a generic function capable of merging aObj into bObj. Let’s start by defining some types we can use as examples, along with an instance of each: I’ve found a way to implement typing when merging objects using some of the new features in TypeScript 2.8. ![]() It’s super convenient and is the best way to merge two dictionaries in newer releases of Python. Object.assign’s typing isn’t as precise as it could be, and spreading generics still doesn’t work. New to Python 3.9, the dictionary union operator lets you merge two dictionaries in a single line. There are times when you want to merge two generic types in TypeScript, and type inference just isn’t doing it for you. ![]()
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