Values and truthiness

#Kinds of values

Kind	Written as	Notes
String	`"text"` or `'text'`	A backslash takes the next character literally: `"say \"hi\""`. There are no escape sequences such as `\n`.
Integer	`42`, `-7`	Exact 64-bit integers.
Decimal	`3.14`, `-0.5`	64-bit floating point. Exponent notation is not accepted.
Boolean	`true`, `false`
Nothing	`nil` or `null`	Prints nothing.
Empty	`empty` or `blank`	Only for comparisons; see Empty.
Range	`(1..5)`	A list of integers; see Loops.
Array, map	from data only	There are no array or map literals.

Template

{{ "double" }} {{ 'single' }} {{ "say \"hi\"" }} {{ 42 }} {{ -0.5 }} {{ true }} [{{ nil }}]

Output

double single say &#34;hi&#34; 42 -0.5 true []

#Integers stay exact

A number without a decimal point is an exact integer, and arithmetic between two integers stays exact. This matters for large identifiers.

Template

{{ 9007199254740993 | plus: 1 }} {{ 10 | divided_by: 4 }} {{ 10 | divided_by: 5 }}

Output

9007199254740994 2.5 2

Division keeps a fractional result. A calculation that overflows 64 bits falls back to floating point. Data from the application keeps its own type: numbers decoded from JSON are floating point.

#Truthiness

Conditions such as {% if %} test whether a value is truthy.

Value	In a condition
`false`	false
`nil`, a missing field	false
`true`	true
`0`, `0.0`	true
`""` (empty string)	true
`[]`, `{}` (empty array or map)	true
any other value	true

Only false and nothing are false. To ask "is there anything here?", compare with blank, or check .size.

Template

{% if settings.zero %}0 is true{% endif %}, {% if settings.text %}"" is true{% endif %}, {% if settings.missing %}{% else %}missing is false{% endif %}

Data

{"settings": {"zero": 0, "text": ""}}

Output

0 is true, "" is true, missing is false

#Empty and blank

empty and blank are the same marker. A value equals it when the value is nothing, an empty string, or a collection with no entries. A string of spaces is not blank.

Template

{% if settings.title == blank %}No title{% endif %} / {% if settings.tags == empty %}No tags{% endif %} / {% if settings.space == blank %}blank{% else %}not blank{% endif %}

Data

{"settings": {"title": "", "tags": [], "space": " "}}

Output

No title / No tags / not blank

#Comparing values

Operator	Meaning
`==`, `!=`	Equal, not equal.
`<`, `>`, `<=`, `>=`	Order. Both sides must be numbers, or both strings.
`contains`	Substring of a string, or member of an array.

Equality is forgiving: numbers compare as numbers, and a string that is a number equals that number. Anything else compares by its printed text.

Template

{{ 1 == 1.0 }} {{ "5" == 5 }} {{ "a" == "a" }} {{ nil == nil }} {{ "1" != 2 }}

Output

true true true true true

Ordering is strict. Comparing a number with a string, or anything that is not a number or string, is an error, never a silent false.

Template

{{ 2 > 1 }} {{ "b" > "a" }} {{ 10 >= 10 }}

Output

true true true

Template

{% if settings.count > "3" %}more{% endif %}

Data

{"settings": {"count": 5}}

Error

cannot compare number and string with ">"

contains looks for a substring in a string, or an equal member in an array. It is always false for maps and other values.

Template

{{ "teapot" contains "tea" }} {{ settings.tags contains "new" }} {{ settings.tags contains "old" }}

Data

{"settings": {"tags": ["new", "sale"]}}

Output

true true false

#How values print

Value	Prints as
String	itself, HTML-escaped
Integer	digits: `42`
Decimal	shortest exact form: `2.5`, `3` for `3.0`
Boolean	`true` or `false`
`nil`	nothing
Array	its items printed one after another, with no separator; use `join`
Map	a debugging form; print its fields instead

Template

{{ settings.list }} | {{ settings.list | join: ", " }} | {{ 3.0 }}

Data

{"settings": {"list": ["a", "b", "c"]}}

Output

abc | a, b, c | 3

Next: Variables, data and scope.