In TypeScript, the return type should match the input type

I am faced with a situation where I have two functions that essentially perform the same task, but differ in the types of their inputs and outputs. I am exploring ways to combine these functions into one, and one potential solution is to use a union type. However, my requirement is that when the input is a member of the union type, the returned value must also be the same type. 

const getViewStyle = (styles: ViewStyle[]): ViewStyle => {
  return Object.assign({}, ...styles);
};

const getTextStyle = (styles: TextStyle[]): TextStyle => {
  return Object.assign({}, ...styles);
};
typescriptunion-types

Answer №1

Here is a possible solution:

One way to achieve this is by using the following function:
const flattenObjectsToSingle = <T>(items: T[]): T => { ...

Answer №2

The optimal approach would be a combination of generic and inferred types. By using this approach, TypeScript's linter can continue to provide feedback if you expect a specific type to be returned from the function.

In my view, the following code snippet represents the ideal solution:

const getStyle = <T extends TextStyle | ViewStyle >(styles: T[]): T => { 
      return Object.assign({}, ...styles);
};

This essentially means that the function anticipates an array of either TextStyle or ViewStyle elements and returns a single record of any given type.

Credit for this solution goes to Ben Awad's video on YouTube: https://www.youtube.com/watch?v=nViEqpgwxHE

Answer №3

I found a solution that has been successful for me thanks to Marius Schulz. You can find the original post by Marius Schulz here: 

function getStyle(styles: ViewStyle[]): ViewStyle;
function getStyle(styles: TextStyle[]): TextStyle;
function getStyle(styles: ViewStyle[] | TextStyle[]): ViewStyle | TextStyle {
    return Object.assign({}, ...styles);
}

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