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99 lines
2.9 KiB
Markdown
99 lines
2.9 KiB
Markdown
+++
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title = "Statements"
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weight = 4
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sort_by = "weight"
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in_search_index = true
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+++
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Expression Statements
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-------
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The simplest and least useful is the expression statement. It is any valid expression
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followed by a semicolon.
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```
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1;
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4 / 2;
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"foo";
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"foo" + "bar";
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```
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Despite the fact that these are valid the results are thrown away and can essentially
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be considered a noop.
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Named Value Statements
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--------
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### Let statements
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There is one statement that can introduce a named value for a given UCG file,
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the let statement. Any collisions in binding names inside a file are treated as
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compile errors. Bindings are immutable and once bound they can't be modified.
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```
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let name = "foo";
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```
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Output Statements
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-----------
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Some statements in UCG exist to generate an output. Either a compiled
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configuration or the results of test assertions.
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### Assert Statements
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The assert statement defines an expression that must evaluate to tuple with an
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ok field that is either true or false and a desc field that is a string. Assert
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statements are noops except when executing `ucg test`. They give you a way to
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assert certains properties about your data and can be used as a form of unit
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testing for your configurations. It starts with the `assert` keyword followed
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by a valid ucg expression that resolves to a tuple with an `ok` field and a
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`desc` field. The `ok` field must contain a boolean value. The `desc` field
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must contain a description for this assertion. The `ok` field is `true` the
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assert test succeeds. When it is `false` the assert test fails.
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```
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assert {
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ok = host == "www.example.com",
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desc = "Host is www.example.com",
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};
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assert {
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ok = select qa, 443, {
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qa = 80,
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prod = 443,
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} == 443,
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desc = "select default was 443",
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};
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```
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Assert statements are only evaluated when running the `ucg test` command. That
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command evaluates all of the `*_test.ucg` files. When `*_test.ucg` files are
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run in a test run then ucg will output a log of all the assertions to stdout as
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well as a PASS or FAIL for each file. This gives you a simple test harness for
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your ucg configs.
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### Out Statements
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The Out statement defines the output for a UCG file. It identifies the output
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converter type and an expression that will be output. The output converter type
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is expected to be one of the registered converters unquoted (e.g. json, exec)
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and the value to convert. The generated artifact will take the same name as
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the UCG file with the extension replaced by the defined extension for that
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converter.
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For a file named api_config.ucg with the following contents:
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```
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let myconf = {
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api_url = "https://example.org/api/v1/",
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api_token = env.API_TOKEN,
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};
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out json myconf;
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```
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UCG will output the myconf tuple as json to a file called api_config.json
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You can get a list of the available converters as well as the extensions
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defined for each one by running the `ucg converters` command.
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Next: <a href="/reference/converters">Converters</a> |