mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-11-27 13:32:56 +03:00
140 lines
4.1 KiB
JSON
140 lines
4.1 KiB
JSON
---
|
|
language: jsonnet
|
|
filename: learnjsonnet.jsonnet
|
|
contributors:
|
|
- ["Huan Wang", "https://github.com/fredwangwang"]
|
|
---
|
|
|
|
Jsonnet is a powerful templating language for JSON. Any valid JSON
|
|
document is a valid Jsonnet object. For an interactive demo/tutorial,
|
|
click [here](https://jsonnet.org/learning/tutorial.html)
|
|
|
|
```python
|
|
// single line comment
|
|
|
|
/*
|
|
multiline comment
|
|
*/
|
|
|
|
# as well as python style comment
|
|
|
|
# define a variable.
|
|
# Variables have no effect in the generated JSON without being used.
|
|
local num1 = 1;
|
|
local num2 = 1 + 1;
|
|
local num3 = 5 - 2;
|
|
local num4 = 9 % 5;
|
|
local num5 = 10 / 2.0;
|
|
# jsonnet is a lazy language, if a variable is not used, it is not evaluated.
|
|
local num_runtime_error = 1 / 0;
|
|
|
|
# fields are valid identifiers without quotes
|
|
local obj1 = { a: 'letter a', B: 'letter B' };
|
|
|
|
local arr1 = ['a', 'b', 'c'];
|
|
|
|
# string literals use " or '.
|
|
local str1 = 'a' + 'B';
|
|
# multiline text literal in between |||
|
|
# Each line must start with a white space.
|
|
local str_multiline = |||
|
|
this is a
|
|
multiline string
|
|
|||;
|
|
# Python-compatible string formatting is available via %
|
|
# When combined with ||| this can be used for templating text files.
|
|
local str_templating = |||
|
|
%(f1)0.3f
|
|
||| % { f1: 1.2345678 };
|
|
assert str_templating == '1.235\n';
|
|
|
|
# if b then e else e. The else branch is optional and defaults to null
|
|
local var1 = if 3 < 2 then "YES";
|
|
assert var1 == null;
|
|
|
|
local obj2 = {
|
|
# variable defined inside the object ends with ','
|
|
local var_in_obj = 0,
|
|
|
|
local vowels = ['a', 'e', 'i', 'o', 'u'],
|
|
local numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
|
|
|
|
# [num] to look up an array element
|
|
first_vowel: vowels[0],
|
|
# can also slice the array like in Python
|
|
even_numbers: numbers[1::2],
|
|
|
|
# python-style list and object comprehensions are also supported
|
|
double_numbers: [x * 2 for x in numbers],
|
|
even_numbers_map: {
|
|
# [ ] syntax in field name is to compute the field name dynamically
|
|
[x + '_is_even']: true for x in numbers if x % 2 == 0
|
|
},
|
|
|
|
nested: {
|
|
nested_field1: 'some-value',
|
|
# self refers to the current object
|
|
# ["field-name"] or .field-name can be used to look up a field
|
|
nested_field2: self.nested_field1,
|
|
nested_field3: self.nested_field1,
|
|
# $ refers to outer-most object
|
|
nested_field4: $.first_vowel,
|
|
|
|
assert self.nested_field1 == self.nested_field2,
|
|
assert self.nested_field1 == self.nested_field3,
|
|
},
|
|
|
|
special_field: 'EVERYTHING FEELS BAD',
|
|
};
|
|
|
|
local obj3 = {
|
|
local var_in_obj = 1.234,
|
|
local var_in_obj2 = { a: { b: 'c' } },
|
|
|
|
concat_array: [1, 2, 3] + [4],
|
|
# strings can be concat with +,
|
|
# which implicitly converts one operand to string if needed.
|
|
concat_string: '123' + 4,
|
|
|
|
# == tests deep equality
|
|
equals: { a: { b: 'c', d: {} } } == var_in_obj2,
|
|
|
|
special_field: 'this feels good',
|
|
};
|
|
|
|
# objects can be merged with + where the right-hand side wins field conflicts
|
|
local obj4 = obj2 + obj3;
|
|
assert obj4.special_field == 'this feels good';
|
|
|
|
# define a function
|
|
# functions have positional parameters, named parameters, and default arguments
|
|
local my_function(x, y, z=1) = x + y - z;
|
|
local num6 = my_function(7, 8, 9);
|
|
local num7 = my_function(8, z=10, y=9);
|
|
local num8 = my_function(4, 5);
|
|
# inline anonymous function
|
|
local num9 = (function(x) x * x)(3);
|
|
|
|
local obj5 = {
|
|
# define a method
|
|
# fields defined with :: are hidden, which does not apper in generated JSON
|
|
# function cannot be serialized so need to be hidden
|
|
# if the object is used in the generated JSON.
|
|
is_odd(x):: x % 2 == 1,
|
|
};
|
|
assert obj5 == {};
|
|
|
|
# a jsonnet document has to evaluate to something
|
|
# be it an object, list, number or just string literal
|
|
"FIN"
|
|
|
|
```
|
|
|
|
## Further Reading
|
|
There are a few but important concepts that are not touched in this exmaple, including:
|
|
|
|
- Passing variables from command line: [Parameterize Entire Config](https://jsonnet.org/learning/tutorial.html#parameterize-entire-config)
|
|
- Import other jsonnet libraries/files: [Imports](https://jsonnet.org/learning/tutorial.html#imports)
|
|
- In depth example of OOP aspect of Jsonnet: [Object-Orientation](https://jsonnet.org/learning/tutorial.html#Object-Orientation)
|
|
- Useful standard library: [Stdlib](https://jsonnet.org/ref/stdlib.html)
|