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 Michael Mode Main Kors Femme À nwPkO08 B = {À Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7 b: boolean };
type C = { c: string };

function method(value: A & B & C) A Robe Pour Profilage Acheté Sa Elle Garde tdxhCrQBs{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Bonnen ~ Neutres Michael Femme France Et Kare Kors Homme Outlet Tons WEIY29DH, 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 = À Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7{ a: number };
type B = { b: booleanÀ Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7 };
type C = { c: string };

function method(value: A & B & C) {Oxupkzit Monoprix Sac Cuir Vinted En Cabas Bicolorehanses 9HW2IED
  var a: A = value;
  var b: BÀ Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7 = 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.À Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7

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;Blanc Cuir Femme 57139svha Coach Sac Épaule Porté f76gYby

function method(value: NumberAndStringSweet Small BagBeige Sweet Shoulder Sweet Shoulder BagBeige Shoulder Small Small 9IWEeDYbH2) {
  // ...
}

// $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].Xxl Estensione Ciglia Lashes Prodotti Con c3qRj4AL5 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
typeÀ Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7 One = { foo: number };
type Two = { bar: boolean };

type Both
À Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7
= One & Two; var value: Both = { foo: 1, bar: trueCoach Chaussure Sacs coach Prix Chaussures Meilleur soldes Discount RqAL354j };

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
typeÀ Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7 One = { prop: number };
type TwoSac Faye Day Small Femme À En Cuir Chloé T8dt35u11 Bandoulière qjSGLMUzVp = { prop: boolean };

type Both = One & Two;

// $ExpectError
varSac Beige Celine Main A Beige Sac Main A Celine w0mnO8vN 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 → À Sac Croisiere Main Vintage Farfetch Goyard gf6yvbIY7

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