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UPDATE - the context of this question was pre-TypeScript 1.4. Since that version, my first guess has been supported by the language. See the update to the answer.
I can declare f to be a function that accepts a string and returns a string:
var f : (string) => string And I can declare g to be an array of string:
var g : string[] How can I declare h to be an array of "function that accepts a string and returns a string"?
My first guess:
var h : ((string) => string)[] That seems to be a syntax error. If I take away the extra parentheses then it's a function from string to array of string.
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To declare a function with an array return type, set the return type of the function to an array right after the function's parameter list, e.g. function getArr(): string[] {} . If the return type of the function is not set, TypeScript will infer it. Copied!
An array in TypeScript can contain elements of different data types using a generic array type syntax, as shown below. let values: (string | number)[] = ['Apple', 2, 'Orange', 3, 4, 'Banana']; // or let values: Array<string | number> = ['Apple', 2, 'Orange', 3, 4, 'Banana'];
In TypeScript, an array is an ordered list of values. An array can store a mixed type of values. To declare an array of a specific type, you use the let arr: type[] syntax.
The function's return type is string. Line function returns a string value to the caller. This is achieved by the return statement. The function greet() returns a string, which is stored in the variable msg.
I figured it out. The problem is that the => for a function type literal is itself merely syntactic sugar and doesn't want to compose with [].
As the spec says:
A function type literal of the form
( ParamList ) => ReturnType
is exactly equivalent to the object type literal
{ ( ParamList ) : ReturnType }
So what I want is:
var h : { (s: string): string; }[] Complete example:
var f : (string) => string f = x => '(' + x + ')'; var h : { (s: string): string; }[] h = []; h.push(f); Update:
Judging from this changeset parentheses will be allowed in type declarations in 1.4, so the "first guess" in the question will also be correct:
var h: ((string) => string)[] Further Update It is in 1.4!
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