dict: Document, add release snippet

docs/markdown/Reference-manual.md

@@ -1730,6 +1730,21 @@ The following methods are defined for all [arrays](Syntax.md#arrays):
 You can also iterate over arrays with the [`foreach`
 statement](Syntax.md#foreach-statements).
 
+### `dictionary` object
+
+The following methods are defined for all [dictionaries](Syntax.md#dictionaries):
+
+- `has_key(key)` returns `true` if the dictionary contains the key
+  given as argument, `false` otherwise
+
+- `get(key, fallback)`, returns the value for the key given as first argument
+  if it is present in the dictionary, or the optional fallback value given
+  as the second argument. If a single argument was given and the key was not
+  found, causes a fatal error
+
+You can also iterate over dictionaries with the [`foreach`
+statement](Syntax.md#foreach-statements).
+
 ## Returned objects
 
 These are objects returned by the [functions listed above](#functions).

docs/markdown/Syntax.md

@@ -284,6 +284,29 @@ The following methods are defined for all arrays:
  - `contains`, returns `true` if the array contains the object given as argument, `false` otherwise
  - `get`, returns the object at the given index, negative indices count from the back of the array, indexing out of bounds is a fatal error. Provided for backwards-compatibility, it is identical to array indexing.
 
+Dictionaries
+--
+
+Dictionaries are delimited by curly braces. A dictionary can contain an
+arbitrary number of key value pairs. Keys are required to be literal
+strings, values can be objects of any type.
+
+```meson
+my_dict = {'foo': 42, 'bar': 'baz'}
+```
+
+Keys must be unique:
+
+```meson
+# This will fail
+my_dict = {'foo': 42, 'foo': 43}
+```
+
+Dictionaries are immutable.
+
+Visit the [Reference Manual](Reference-manual.md#dictionary-object) to read
+about the methods exposed by dictionaries.
+
 Function calls
 --
 
@@ -329,9 +352,17 @@ endif
 
 ## Foreach statements
 
-To do an operation on all elements of an array, use the `foreach`
-command. As an example, here's how you would define two executables
-with corresponding tests.
+To do an operation on all elements of an iterable, use the `foreach`
+command.
+
+> Note that Meson variables are immutable. Trying to assign a new value
+> to the iterated object inside a foreach loop will not affect foreach's
+> control flow.
+
+### Foreach with an array
+
+Here's an example of how you could define two executables
+with corresponding tests using arrays and foreach.
 
 ```meson
 progs = [['prog1', ['prog1.c', 'foo.c']],
@@ -343,9 +374,30 @@ foreach p : progs
 endforeach
 ```
 
-Note that Meson variables are immutable. Trying to assign a new value
-to `progs` inside a foreach loop will not affect foreach's control
-flow.
+### Foreach with a dictionary
+
+Here's an example of you could iterate a set of components that
+should be compiled in according to some configuration.
+
+```meson
+components = {
+  'foo': ['foo.c'],
+  'bar': ['bar.c'],
+  'baz:' ['baz.c'],
+}
+
+# compute a configuration based on system dependencies, custom logic
+conf = configuration_data()
+conf.set('USE_FOO', 1)
+
+# Determine the sources to compile
+sources_to_compile = []
+foreach name, sources : components
+  if conf.get('USE_@0@'.format(name.to_upper()), 0) == 1
+    sources_to_compile += sources
+  endif
+endforeach
+```
 
 Logical operations
 --

docs/markdown/snippets/dict_builtin.md

@@ -0,0 +1,19 @@
+## New built-in object dictionary
+
+Meson dictionaries use a syntax similar to python's dictionaries,
+but have a narrower scope: they are immutable, keys can only
+be string literals, and initializing a dictionary with duplicate
+keys causes a fatal error.
+
+Example usage:
+
+```meson
+dict = {'foo': 42, 'bar': 'baz'}
+
+foo = dict.get('foo')
+foobar = dict.get('foobar', 'fallback-value')
+
+foreach key, value : dict
+  # Do something with key and value
+#endforeach
+```