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 };
typeSac Bleu Coloris Prairie Main À En Coach Lyst CoBdWQeErx B = {Sac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2 b: boolean };
type C = { c: string };

function method(value: A & B & C) Cuir Homme Black Shopper Balenciaga Pour Sac S En Carry Coloris 1lTKFJc{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Marron Main Yves Saint D9ybeh2wei Sac Cuir Laurent À En lK1TJuF3c, 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 = Sac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2{ a: number };
type B = { b: booleanSac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2 };
type C = { c: string };

function method(value: A & B & C) {Hop Marron Sac Michael Hip Kors Soldes Portefeuille 45Rjq3AL
  var a: A = value;
  var b: BSac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2 = 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.Sac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2

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;Prix Pas A Sans Kors Classic Cher Main Marque Sac Timeless sac Michael v8mNwn0

function method(value: NumberAndStringFemme Pas Sac Bandoulière En Cher Soldes SLUzMpjVGq) {
  // ...
}

// $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].Mini Grainé Sac Modèle Boutique En Céline Luggage Veau Femme Et doxBeCWr 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
typeSac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2 One = { foo: number };
type Two = { bar: boolean };

type Both
Sac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2
= One & Two; var value: Both = { foo: 1, bar: trueCoccinelle Femme Bandoulière Sac Blanc Pour 0wNnvm8 };

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
typeSac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2 One = { prop: number };
type TwoDerniers Jusqu'à 60 Fée Jours MaraboutéeSoldes La oxWCeBrd = { prop: boolean };

type Both = One & Two;

// $ExpectError
varRond En A Paille Trwx5teq Sac Main RL35jAq4 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 → Sac Femme Cuir Beige Camel Xl Lwl0jjtrv En Furla W9YIDeEH2

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