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Define Array.isArray using a type predicate #3492

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Merged
merged 1 commit into from
Jun 13, 2015
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Define Array.isArray using a type predicate #3492

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2 changes: 1 addition & 1 deletion src/lib/core.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1150,7 +1150,7 @@ interface ArrayConstructor {
(arrayLength?: number): any[];
<T>(arrayLength: number): T[];
<T>(...items: T[]): T[];
isArray(arg: any): boolean;
isArray(arg: any): arg is Array<any>;
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could we allow this to be generic? i.e.

isArray<T>(arg: any): arg is Array<T>

?

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We could, but we should add a separate overload for it. Otherwise, not passing the type argument gives you Array<{}>

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so are you expecting this to work:

var arr: Array<number> | Array<string>;

if (Array.isArray<number>(arr)) {
    arr[0].toFixed(); // but what does that mean at runtime?
}

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@mhegazy I think you're right. Specifying the type is claiming to know something that you don't.

prototype: Array<any>;
}

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19 changes: 19 additions & 0 deletions tests/baselines/reference/isArray.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
//// [isArray.ts]
var maybeArray: number | number[];


if (Array.isArray(maybeArray)) {
maybeArray.length; // OK
}
else {
maybeArray.toFixed(); // OK
}

//// [isArray.js]
var maybeArray;
if (Array.isArray(maybeArray)) {
maybeArray.length; // OK
}
else {
maybeArray.toFixed(); // OK
}
22 changes: 22 additions & 0 deletions tests/baselines/reference/isArray.symbols
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@@ -0,0 +1,22 @@
=== tests/cases/compiler/isArray.ts ===
var maybeArray: number | number[];
>maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))


if (Array.isArray(maybeArray)) {
>Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.d.ts, 1166, 28))
>Array : Symbol(Array, Decl(lib.d.ts, 1000, 23), Decl(lib.d.ts, 1171, 11))
>isArray : Symbol(ArrayConstructor.isArray, Decl(lib.d.ts, 1166, 28))
>maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))

maybeArray.length; // OK
>maybeArray.length : Symbol(Array.length, Decl(lib.d.ts, 1007, 20))
>maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))
>length : Symbol(Array.length, Decl(lib.d.ts, 1007, 20))
}
else {
maybeArray.toFixed(); // OK
>maybeArray.toFixed : Symbol(Number.toFixed, Decl(lib.d.ts, 463, 37))
>maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))
>toFixed : Symbol(Number.toFixed, Decl(lib.d.ts, 463, 37))
}
24 changes: 24 additions & 0 deletions tests/baselines/reference/isArray.types
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@@ -0,0 +1,24 @@
=== tests/cases/compiler/isArray.ts ===
var maybeArray: number | number[];
>maybeArray : number | number[]


if (Array.isArray(maybeArray)) {
>Array.isArray(maybeArray) : boolean
>Array.isArray : (arg: any) => boolean
>Array : ArrayConstructor
>isArray : (arg: any) => boolean
>maybeArray : number | number[]

maybeArray.length; // OK
>maybeArray.length : number
>maybeArray : number[]
>length : number
}
else {
maybeArray.toFixed(); // OK
>maybeArray.toFixed() : string
>maybeArray.toFixed : (fractionDigits?: number) => string
>maybeArray : number
>toFixed : (fractionDigits?: number) => string
}
12 changes: 6 additions & 6 deletions tests/baselines/reference/library_ArraySlice.symbols
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Expand Up @@ -2,22 +2,22 @@
// Array.prototype.slice can have zero, one, or two arguments
Array.prototype.slice();
>Array.prototype.slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>Array : Symbol(Array, Decl(lib.d.ts, 1000, 23), Decl(lib.d.ts, 1171, 11))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))

Array.prototype.slice(0);
>Array.prototype.slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>Array : Symbol(Array, Decl(lib.d.ts, 1000, 23), Decl(lib.d.ts, 1171, 11))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))

Array.prototype.slice(0, 1);
>Array.prototype.slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>Array : Symbol(Array, Decl(lib.d.ts, 1000, 23), Decl(lib.d.ts, 1171, 11))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>slice : Symbol(Array.slice, Decl(lib.d.ts, 1048, 15))

4 changes: 2 additions & 2 deletions tests/baselines/reference/returnTypeParameterWithModules.symbols
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Expand Up @@ -14,9 +14,9 @@ module M1 {
return Array.prototype.reduce.apply(ar, e ? [f, e] : [f]);
>Array.prototype.reduce.apply : Symbol(Function.apply, Decl(lib.d.ts, 228, 20))
>Array.prototype.reduce : Symbol(Array.reduce, Decl(lib.d.ts, 1129, 93), Decl(lib.d.ts, 1136, 120))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>Array.prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>Array : Symbol(Array, Decl(lib.d.ts, 1000, 23), Decl(lib.d.ts, 1171, 11))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 31))
>prototype : Symbol(ArrayConstructor.prototype, Decl(lib.d.ts, 1167, 41))
>reduce : Symbol(Array.reduce, Decl(lib.d.ts, 1129, 93), Decl(lib.d.ts, 1136, 120))
>apply : Symbol(Function.apply, Decl(lib.d.ts, 228, 20))
>ar : Symbol(ar, Decl(returnTypeParameterWithModules.ts, 1, 30))
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9 changes: 9 additions & 0 deletions tests/cases/compiler/isArray.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
var maybeArray: number | number[];


if (Array.isArray(maybeArray)) {
maybeArray.length; // OK
}
else {
maybeArray.toFixed(); // OK
}