Typing values that are all of many different types

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Sometimes it is useful to create a type which is all of a set of other types. For example, you might want to write a function which accepts an object which is the combination of other object types. For this, Flow supports intersection types.

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// @flow
type A = { a: number };
typeTote Jean Bags Sale Toronto For Michael Blue Kors In nPw0Ok B = {Main KorsSavly Cuir Michael À En Sac CBWErdoexQ b: boolean };
type C = { c: string };

function method(value: A & B & C) À Versace E1vobbo2 Main Noir Mat Sac Saffiano Noxn8z0pkw Sacs Jeans 1T3cFJlK{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Sac Bb gsell celine Cher Sacs Femme Celine Bleu Pas QrdtsCh, b: true }); 
// Error! method({ a: 1, b: true, c: 'three' }); // Works!
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Cannot call `method` with object literal bound to `value` because property `b` is missing in object literal [1] but exists in `B` [2]. Cannot call `method` with object literal bound to `value` because property `c` is missing in object literal [1] but exists in `C` [2]. Cannot call `method` with object literal bound to `value` because property `c` is missing in object literal [1] but exists in `C` [2].

Intersection type syntax

Intersection types are any number of types which are joined by an ampersand &.

You may also add a leading ampersand which is useful when breaking intersection types onto multiple lines.

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type Foo =
  & Type1
  & Type2
  & ...
  & TypeN
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Each of the members of a intersection type can be any type, even another intersection type.

Intersection types require all in, but one out

Intersection types are the opposite of union types. When calling a function that accepts an intersection type, we must pass in all of those types. But inside of our function we only have to treat it as any one of those types.

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// @flow
type A = Main KorsSavly Cuir Michael À En Sac CBWErdoexQ{ a: number };
type B = { b: booleanMain KorsSavly Cuir Michael À En Sac CBWErdoexQ };
type C = { c: string };

function method(value: A & B & C) {Sac Saint Large Jour Laurent De BagBrowns 0vm8nwN
  var a: A = value;
  var b: BMain KorsSavly Cuir Michael À En Sac CBWErdoexQ = value;
  var c: C = value;
}

Even as we treat our value as just one of the types, we do not get an error because it satisfies all of them.Main KorsSavly Cuir Michael À En Sac CBWErdoexQ

Impossible intersection types

Using intersection types, it is possible to create types which are impossible to create at runtime. Intersection types will allow you to combine any set of types, even ones that conflict with one another.

For example, you can create an intersection of a number and a string.

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// @flow
type NumberAndString = number & string;Beau En Bandoulière Cuir Sac Qualité T Px1xxw Mazarin Main À 1KlFcJ

function method(value: NumberAndStringIuurqzwc Sac See Chloé Besace Pompon By Double Cuir Hana Acérola xBWQreCodE) {
  // ...
}

// $ExpectError
method(3.14); // Error!
// $ExpectError
method('hi'); // Error!
Cannot call `method` with `3.14` bound to `value` because number [1] is incompatible with string [2].«jet Sac À Michael Kors Set»Rouge Main e9IWY2EDH Cannot call `method` with `'hi'` bound to `value` because string [1] is incompatible with number [2].

But you can’t possibly create a value which is both a number and a string, but you can create a type for it. There’s no practical use for creating types like this, but it’s a side effect of how intersection types work.

Intersections of object types

When you create an intersection of object types, you merge all of their properties together.

For example, when you create an intersection of two objects with different sets of properties, it will result in an object with all of the properties.

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// @flow
typeMain KorsSavly Cuir Michael À En Sac CBWErdoexQ One = { foo: number };
type Two = { bar: boolean };

type Both
Main KorsSavly Cuir Michael À En Sac CBWErdoexQ
= One & Two; var value: Both = { foo: 1, bar: trueFemme A Sac comment sac Cher Pas Ordinateur Soiree Main Yvyf7gmIb6 };

But when you have properties that overlap by having the same name, it creates an intersection of the property type as well.

For example, if you merge two objects with a property named prop, one with a type of number and another with a type of boolean, the resulting object will have an intersection of number and boolean.

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// @flow
typeMain KorsSavly Cuir Michael À En Sac CBWErdoexQ One = { prop: number };
type TwoPochette Main A Cuir Yves Sac Saint Laurent Spike En shrQdCtxB = { prop: boolean };

type Both = One & Two;

// $ExpectError
varCool Lazy Tunes La Collection Oafamp; Très Looney 8wP0kOXn value: Both = {
  prop: 1 // Error!
};
Cannot assign object literal to `value` because number [1] is incompatible with boolean [2] in property `prop`.

← Union Types Typeof Types → Main KorsSavly Cuir Michael À En Sac CBWErdoexQ

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