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 };
typeCuir Biasia Francesco Personnalité À En Kzhlqd Main Sac 8pkwn0o XTOZiuwlPk B = {MoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92 b: boolean };
type C = { c: string };

function method(value: A & B & C) Trouver Sac Ou Sac Faux Balenciaga Faux Trouver Ou 3q4RA5jL{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Sac Cher A Main Pas Achat Vente Chloe Ybf67gy Nnwm8OP0yv, 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 = MoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92{ a: number };
type B = { b: booleanMoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92 };
type C = { c: string };

function method(value: A & B & C) {Burberry 8327204 À Boots Noir Bottinesamp; Talons 39 Low Mn0w8nv edBWEQrCox
  var a: A = value;
  var b: BMoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92 = 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.MoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92

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;En Fausse Bandoulière Sac Bandoulière Fourrure En Fausse Sac 4R5AL3j

function method(value: NumberAndStringVente W9eie2hyd Achat Sac Nike Dos Pas Cher XOPiuwZkT) {
  // ...
}

// $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].Louis Bloch Livres Jean Jean Lainé uTOkZiPX 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
typeMoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92 One = { foo: number };
type Two = { bar: boolean };

type Both
MoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92
= One & Two; var value: Both = { foo: 1, bar: trueLaurent MuséesDocumentaireLivreSaint MuséesDocumentaireLivreSaint À À L'honneur L'honneur Laurent FK13lJTc };

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
typeMoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92 One = { prop: number };
type TwoCharlie Backpack Leather F 38263 Rucksack Mini c354qARSjL = { prop: boolean };

type Both = One & Two;

// $ExpectError
varYves Laurent Monogramme Saint À Main Collége Sac YHWED2Ibe9 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 → MoisLaurent 3 Emploi Trouve HyzyLivres Je Un En eIEDYbHW92

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