How to define in TypeScript interface for merge function?

Question

There are some way to define such interface for merge function:

interface mergeFunc<T, S, P exntends T,S>(t:T, s:S):P;

var merge:mergeFunc = function (t:any, s:any):any {
   var res = {};
   for (let x in t) res[x] = t[x];
   for (let x in s) res[x] = s[x];
   return res;
}

?

Ryan Cavanaugh · Accepted Answer · 2015-08-04 17:10:10Z

2

In TypeScript 1.6 (or TypeScript nightly today, use npm install typescript@next), you'll be able to use intersection types to write this:

declare function mergeFunc<T, S>(t:T, s:S): T & S;

See https://github.com/Microsoft/TypeScript/pull/3622

answered Aug 4, 2015 at 17:10

Ryan Cavanaugh

223k59 gold badges280 silver badges235 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Gaspard Bucher · Accepted Answer · 2016-04-08 08:08:05Z

0

For immutable change of T

If you only need to merge properties compatible with the initial type, since TypeScript 1.8 you can use type parameters as constraints :

const merge = function<T extends S, S>
( t: T, s: S ) : T {
  const res: any = {}
  // copy
  for ( const k in t ) {
    if ( t.hasOwnProperty ( k ) ) {
      res [ k ] = t [ k ]
    }
  }
  // merge
  for ( const k in s ) {
    if ( s.hasOwnProperty ( k ) ) {
      res [ k ] = s [ k ]
    }
  }
  return res
}

edited Apr 8, 2016 at 8:08

answered Apr 8, 2016 at 7:50

Gaspard Bucher

6,1475 gold badges43 silver badges55 bronze badges

Collectives™ on Stack Overflow

How to define in TypeScript interface for merge function?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related