Functions

Functions are introduced by the func keyword.

Return type, if any, comes after parameters. The return does as you expect.

func square(f float) float { return f*f }

A function can return multiple values. If so, the return types are a parenthesized list.

func MySqrt(f float) (float, bool) {

if f >= 0 { return math.Sqrt(f), true }

return 0, false

}

Functions with result variables

The result “parameters” are actual variables you can use if you name them.

func MySqrt(f float) (v float, ok bool) {

if f >= 0 { v,ok = math.Sqrt(f),true }

else { v,ok = 0,false }

return v,ok

}

The result variables are initialized to “zero”

(0,0.0, false etc. according to type; more in a sec).

func MySqrt(f float) (v float, ok bool) {

if f >= 0 { v,ok = math.Sqrt(f),true }

return v,ok

}

The empty return

Finally, a return with no expressions returns the existing value of the result variables. Two more versions of MySqrt:

func MySqrt(f float) (v float, ok bool) {

if f >= 0 { v,ok = math.Sqrt(f),true }

return // must be explicit

}

func MySqrt(f float) (v float, ok bool) {

if f < 0 { return } // error case

return math.Sqrt(f),true

}

Function literals

As in C, functions can’t be declared inside functions -but function literals can be assigned to variables.

func f() {

for i := 0; i < 10; i++ {

g := func(i int) { fmt.Printf(”%d”,i) };

g(i);

}

}

Function literals are closures

Function literals are indeed closures.

func adder() (func(int) int) {

var x int;

return func(delta int) int {

x += delta;

return x

}

}

var f = adder();

fmt.Print(f(1));

fmt.Print(f(20));

fmt.Print(f(300));

Prints 1 21 321 – accumulating in f’s x

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