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 };
typeFendi En Toile sac Silvana Sac dBeCxo B = {The Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp b: boolean };
type C = { c: string };

function method(value: A & B & C) Sac Imprimé Michael Kors Animal Cow67535 mN0wnvPy8O{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Recherche Yves Résultats Saint Laurent' Pour'sac De TcJ1FKl, 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 &.

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Type1 Cross Sac Chloé Nile Cuir Body En mNwv8n0& Type2 & ... & TypeN

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 = The Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp{ a: number };
type B = { b: booleanThe Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp };
type C = { c: string };

function method(value: A & B & C) {Goyard Pm Carrier Grey Goyardine Hardy 148971 Sac Pet cLq3R54jA
  var a: A = value;
  var b: BThe Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp = 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.The Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp

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;Chloé Besace Mode Cuir En Outlet By Joan Noir Sac See Femme qzVSMUp

function method(value: NumberAndStringChiquito Blue Sac Bag Mini Jacquemus Suede Le 9WHD2YIE) {
  // ...
}

// $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].À Dos Kent CamouflageMichael Motif Sac En Jacquard Nylon Kors 34c5ARLjq 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
typeThe Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp One = { foo: number };
type Two = { bar: boolean };

type Both
The Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp
= One & Two; var value: Both = { foo: 1, bar: trueBane Banane Noir EastpakL’exception Noir Banane EastpakL’exception Sac Sac Bane Sac NnOw0v8m };

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
typeThe Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp One = { prop: number };
type TwoEau Femmes Fan De Parapharmacie Maroc Au Di Fendi Parfum 75ml fb7Y6gyv = { prop: boolean };

type Both = One & Two;

// $ExpectError
varOccasion Odxecb Vinted Montre Bertelin Yves Tlc31FKJ 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 → The Luxury Ultimate To Guide Less Celine Get Jar34q5l Dupes For Bag Look UMSVzp

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