xgo/docs/builtins.md

Builtin Functions

print

Prints a string representation of the given variable to the standard output.

v := [1, 2, 3]
print(v)  // "[1, 2, 3]"

print(1, 2, 3)
// "1"
// "2"
// "3"

printf

Prints a formatted string to the standard output. It does not append the newline character at the end. The first argument must a String object. It's same as Go's fmt.Printf.

a := [1, 2, 3]
printf("foo %v", a)  // "foo [1, 2, 3]"

sprintf

Returns a formatted string. The first argument must be a String object. It's the same as Go's fmt.Sprintf.

a := [1, 2, 3]
b := sprintp("foo %v", a)  // b == "foo [1, 2, 3]" 

len

Returns the number of elements if the given variable is array, string, map, or module map.

v := [1, 2, 3]
l := len(v) // l == 3

copy

Creates a copy of the given variable. copy function calls Object.Copy interface method, which is expected to return a deep-copy of the value it holds.

v1 := [1, 2, 3]
v2 := v1
v3 := copy(v1)
v1[1] = 0
print(v2[1]) // "0"; 'v1' and 'v2' referencing the same array
print(v3[1]) // "2"; 'v3' not affected by 'v1'

append

Appends object(s) to an array (first argument) and returns a new array object. (Like Go's append builtin.) Currently, this function takes array type only.

v := [1]
v = append(v, 2, 3) // v == [1, 2, 3]

to_json

Returns the JSON encoding of an object.

print(to_json([1, 2, 3]))  // [1, 2, 3]
print(to_json(4))          // 4
print(to_json("five"))     // "five"

from_json

Parses the JSON-encoded data and returns an object.

arr := from_json(`[1, 2, 3]`)
four := from_json(`4`)
five := from_json(`"five"`)

string

Tries to convert an object to string object. See Runtime Types for more details on type conversion.

x := string(123) //  v == "123"

type_name

Returns the type_name of an object.

type_name(1) // int
type_name("str") // string
type_name([1, 2, 3]) // array

Optionally it can take the second argument, which will be returned if the first argument cannot be converted to string. Note that the second argument does not have to be string.

v = string(undefined, "foo")  // v == "foo"
v = string(undefined, false)  // v == false 

int

Tries to convert an object to int object. See this for more details on type conversion.

v := int("123") //  v == 123

Optionally it can take the second argument, which will be returned if the first argument cannot be converted to int. Note that the second argument does not have to be int.

v = int(undefined, 10)    // v == 10
v = int(undefined, false) // v == false 

bool

Tries to convert an object to bool object. See this for more details on type conversion.

v := bool(1) //  v == true

float

Tries to convert an object to float object. See this for more details on type conversion.

v := float("19.84") //  v == 19.84

Optionally it can take the second argument, which will be returned if the first argument cannot be converted to float. Note that the second argument does not have to be float.

v = float(undefined, 19.84)    // v == 19.84
v = float(undefined, false)    // v == false 

char

Tries to convert an object to char object. See this for more details on type conversion.

v := char(89) //  v == 'Y'

Optionally it can take the second argument, which will be returned if the first argument cannot be converted to float. Note that the second argument does not have to be float.

v = char(undefined, 'X')    // v == 'X'
v = char(undefined, false)  // v == false 

bytes

Tries to convert an object to bytes object. See this for more details on type conversion.

v := bytes("foo") //  v == [102 111 111]

Optionally it can take the second argument, which will be returned if the first argument cannot be converted to float. Note that the second argument does not have to be float.

v = bytes(undefined, bytes("foo"))    // v == bytes("foo")
v = bytes(undefined, false)           // v == false 

If you pass an int to bytes() function, it will create a new byte object with the given size.

v := bytes(100)

is_string

Returns true if the object's type is string. Or it returns false.

is_int

Returns true if the object's type is int. Or it returns false.

is_bool

Returns true if the object's type is bool. Or it returns false.

is_float

Returns true if the object's type is float. Or it returns false.

is_char

Returns true if the object's type is char. Or it returns false.

is_bytes

Returns true if the object's type is bytes. Or it returns false.

is_error

Returns true if the object's type is error. Or it returns false.

is_undefined

Returns true if the object's type is undefined. Or it returns false.

is_function

Returns true if the object's type is function or closure. Or it returns false. Note that is_function returns false for builtin functions and user-provided callable objects.

is_callable

Returns true if the object is callable (e.g. function, closure, builtin function, or user-provided callable objects). Or it returns false.