# Tengo Runtime Types

- **Int**: signed 64bit integer
- **String**: string
- **Float**: 64bit floating point
- **Bool**: boolean
- **Char**: character (`rune` in Go)
- **Bytes**: byte array (`[]byte` in Go)
- **Array**: objects array (`[]Object` in Go)
- **ImmutableArray**: immutable object array (`[]Object` in Go)
- **Map**: objects map with string keys (`map[string]Object` in Go)
- **ImmutableMap**: immutable object map with string keys (`map[string]Object`
  in Go)
- **Time**: time (`time.Time` in Go)
- **Error**: an error with underlying Object value of any type
- **Undefined**: undefined

## Type Conversion/Coercion Table

|src\dst  |Int      |String        |Float    |Bool      |Char   |Bytes  |Array  |Map    |Time   |Error  |Undefined|
| :---:   | :---:   | :---:        | :---:   | :---:    | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
|Int      |   -     |_strconv_     |float64(v)|!IsFalsy()| rune(v)|**X**|**X**|**X**|_time.Unix()_|**X**|**X**|
|String   |_strconv_|   -          |_strconv_|!IsFalsy()|**X**|[]byte(s)|**X**|**X**|**X**|**X**|**X**|
|Float    |int64(f) |_strconv_     | -       |!IsFalsy()|**X**|**X**|**X**|**X**|**X**|**X**|**X**|
|Bool     |1 / 0    |"true" / "false"|**X**    |   -   |**X**|**X**|**X**|**X**|**X**|**X**|**X**|
|Char     |int64(c) |string(c)     |**X**    |!IsFalsy()|   -   |**X**|**X**|**X**|**X**|**X**|**X**|
|Bytes    |**X**    |string(y)|**X**    |!IsFalsy()|**X**|   -   |**X**|**X**|**X**|**X**|**X**|
|Array    |**X**    |"[...]"       |**X**    |!IsFalsy()|**X**|**X**|   -   |**X**|**X**|**X**|**X**|
|Map      |**X**    |"{...}"       |**X**    |!IsFalsy()|**X**|**X**|**X**|   -   |**X**|**X**|**X**|
|Time     |**X**    |String()      |**X**    |!IsFalsy()|**X**|**X**|**X**|**X**|   -   |**X**|**X**|
|Error    |**X**    |"error: ..."  |**X**    |false|**X**|**X**|**X**|**X**|**X**|   -   |**X**|
|Undefined|**X**    |**X**|**X**    |false|**X**|**X**|**X**|**X**|**X**|**X**|   -    |

_* **X**: No conversion; Typed value functions for `Variable` will
return zero values._  
_* strconv: converted using Go's conversion functions from `strconv` package._  
_* IsFalsy(): use [Object.IsFalsy()](#objectisfalsy) function_  
_* String(): use `Object.String()` function_
_* time.Unix(): use `time.Unix(v, 0)` to convert to Time_

## Object.IsFalsy()

`Object.IsFalsy()` interface method is used to determine if a given value
should evaluate to `false` (e.g. for condition expression of `if` statement).

- **Int**: `n == 0`
- **String**: `len(s) == 0`
- **Float**: `isNaN(f)`
- **Bool**: `!b`
- **Char**: `c == 0`
- **Bytes**: `len(bytes) == 0`
- **Array**: `len(arr) == 0`
- **Map**: `len(map) == 0`
- **Time**: `Time.IsZero()`
- **Error**: `true` _(Error is always falsy)_
- **Undefined**: `true` _(Undefined is always falsy)_

## Type Conversion Builtin Functions

- `string(x)`: tries to convert `x` into string; returns `undefined` if failed
- `int(x)`: tries to convert `x` into int; returns `undefined` if failed
- `bool(x)`: tries to convert `x` into bool; returns `undefined` if failed
- `float(x)`: tries to convert `x` into float; returns `undefined` if failed
- `char(x)`: tries to convert `x` into char; returns `undefined` if failed
- `bytes(x)`: tries to convert `x` into bytes; returns `undefined` if failed
  - `bytes(N)`: as a special case this will create a Bytes variable with the
  given size `N` (only if `N` is int)
- `time(x)`: tries to convert `x` into time; returns `undefined` if failed
- See [Builtins](https://github.com/d5/tengo/blob/master/docs/builtins.md) for
the full list of builtin functions.

## Type Checking Builtin Functions

- `is_string(x)`: returns `true` if `x` is string; `false` otherwise
- `is_int(x)`: returns `true` if `x` is int; `false` otherwise
- `is_bool(x)`: returns `true` if `x` is bool; `false` otherwise
- `is_float(x)`: returns `true` if `x` is float; `false` otherwise
- `is_char(x)`: returns `true` if `x` is char; `false` otherwise
- `is_bytes(x)`: returns `true` if `x` is bytes; `false` otherwise
- `is_array(x)`: return `true` if `x` is array; `false` otherwise
- `is_immutable_array(x)`: return `true` if `x` is immutable array; `false`
  otherwise
- `is_map(x)`: return `true` if `x` is map; `false` otherwise
- `is_immutable_map(x)`: return `true` if `x` is immutable map; `false`
  otherwise
- `is_time(x)`: return `true` if `x` is time; `false` otherwise
- `is_error(x)`: returns `true` if `x` is error; `false` otherwise
- `is_undefined(x)`: returns `true` if `x` is undefined; `false` otherwise
- See [Builtins](https://github.com/d5/tengo/blob/master/docs/builtins.md) for
  the full list of builtin functions.