--- name: "meson.build" section: "5" platform: "linux" package: "muon-meson" version: "0.4.0-1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/meson.build" --- # meson.build(5) a build system dsl ## NAME meson.build - a build system dsl ## DESCRIPTION The meson dsl is a dynamically typed language, similar to other interpreted languages like python and ruby. All objects are immutable. Functions cannot be defined, only built-in functions are available. - • **STRUCTURE** - overview of source and project layout - • **TYPES** - information on all primitive types - • **SYNTAX** - description of syntax and keywords ## STRUCTURE All meson projects must have a file called \`meson.build\` at the project root. This is the root build file. This file must have a call to the \`project()\` function as its first statement. Additional \`meson.build\` files may reside in any subdirectories of the project. These build files are then executed with the \`subdir()\` function. ## TYPES The meson build system dsl contains most of the common types that would be expected: - • booleans (written as \`true\` and \`false\`) - • integers - • strings - • arrays - • dictionaries ### Booleans Booleans are either \`true\` or \`false\`. **OPERATORS** - • \`and\` - logical and - • \`or\` - logical or - • \`not\` - logical and ### Integers You can specify an integer literal using decimal, hexadecimal, octal, and binary. ``` int_1 = 1 int_42 = 42 int_255 = 0xFF int_493 = 0o755 int_1365 = 0b10101010101 ``` All common arithmetic operations are implemented for integers: addition, subtraction, division, multiplication, and modulo. **OPERATORS** - • \`\*\` - multiplication - • \`/\` - integer division - • \`%\` - modulo (remainder) - • \`+\` - addition - • \`-\` - subtraction - • \`==\` - equal to - • \`!=\` - not equal to - • \`\<\` - less than - • \`\>\` - greater than - • \`\<=\` - less than or equal to - • \`\>=\` - greater than or equal to ### Strings Strings in Meson are declared with single quotes. \`\` is the escape character. The full list of escape sequences is: - • \`\\\` Backslash - • \`'\` Single quote - • \`a\` Bell - • \`b\` Backspace - • \`f\` Formfeed - • \`n\` Newline - • \`r\` Carriage Return - • \`t\` Horizontal Tab - • \`v\` Vertical Tab - • \`ooo\` Character with octal value ooo, up to 3 digits long - • \`xhh\` Character with hex value hh - • \`uxxxx\` Character with 16-bit hex value xxxx - • \`Uxxxxxxxx\` Character with 32-bit hex value xxxxxxxx - • \`N{name}\` Character named name in Unicode database Multi-line strings are surrounded by 3 consecutive quotes. These are raw strings that do not support the escape sequences listed above. Format strings are expressed by a placing leading \`f\` before the first opening quote. Inside of a format string, sequences of the form \`@\[a-z\_\]+@\` will be substituted with the value of the matching variable. This variable can be of type bool, int, or str. ``` name = 'Alice' # prints "Hello Alice" message(f'Hello @name@') ``` **OPERATORS** - • \`+\` - concatenate two strings - • \`/\` - concatenate two strings as if \`join\_paths()\` was called - • \`\[int\]\` - access the character at index - • \`\ in \\` - check if str is a substring - • \`\ not in \\` - check if str is not a substring - • \`==\` - equal to - • \`!=\` - not equal to ### Arrays Arrays are delimited by brackets. An array can contain an arbitrary number of objects of any type. **OPERATORS** - • \`+\` - If the rhs operand is an array, it will be joined to the lhs array. If it is a scalar, it will be appended to the lhs array. - • \`\[int\]\` - access the object at index - • \`\ in \\` - check if object is in \`array\` - • \`\ not in \\` - check if object is not in \`array\` - • \`==\` - equal to - • \`!=\` - not equal to ### Dictionaries Dictionaries are delimited by curly braces. A dictionary can contain an arbitrary number of key: value pairs. Keys are required to be strings, but values can be objects of any type. Dictionaries are immutable and do not have a guaranteed order. **OPERATORS** - • \`+\` - merge two dictionaries. In case of a conflicting key, the value from the rhs dictionary will be taken. - • \`\[str\]\` - access the object with key \`key\` - • \`\ in \\` - check if key is in \`dict\` - • \`\ not in \\` - check if key is not in \`dict\` - • \`==\` - equal to - • \`!=\` - not equal to ## SYNTAX A meson build file is composed of statements, which are terminated by newlines. Other than the statement-terminating newline, white space has no syntactic meaning. ### Comments A comment starts with the \`#\` character and extends until the end of the line. ### Variables A variable can contain a value of any type, and does not need to be predeclared. ``` var1 = 'hello' var2 = 102 ``` One important difference in how variables work in the dsl is that all objects are immutable. When you see an operation which appears like a mutation, actually a new object is created and assigned to the name. ``` var1 = [1, 2, 3] var2 = var1 var2 += [4] # var2 is now [1, 2, 3, 4] # var1 is still [1, 2, 3] ``` ### Function and method calls Builtin functions are called by their name followed by parenthesis containing optional, comma-separated arguments. Arguments are either positional or keyword. Keyword arguments are expressed using the keyword without quotes, followed by a colon. ``` foo() foo('bar') foo('bar', baz: true) ``` Method calls are expressed by a \`.\` followed by the same function call syntax as above. ``` foo.bar() foo.bar('baz', qux: false) ``` For a complete list of functions and methods, please see \`[meson-reference(3)](/meson-reference/3.md)\`. ### If statements Start an if statement with the \`if\` keyword followed by a boolean expression. Further conditions can be expressed using the \`elif\` keyword followed by a boolean expression. The \`else\` keyword can be used to handle the case when no conditions are matched. An if statement is terminated with the \`endif\` keyword. ``` if conditon1 ... elif condition2 ... else condition3 ... endif ``` ### Foreach statements To loop over values in an iterable, use the \`foreach\` keyword followed by a comma separated list of names to assign the values of the iterable to, a colon, and an iterable expression. Only arrays and dictionaries are iterable. A foreach statement is terminated with the \`endforeach\` keyword. Arrays have one value to assign to. ``` foreach value : array foo(value) endforeach ``` Dictionaries have one two values to assign to. ``` foreach key, value : dictionary foo(key) bar(value) endforeach ``` Inside a \`foreach\` block you may use the \`break\` and \`continue\` keywords. \`break\` exits the loop immediately. \`continue\` skips the rest of the current iteration. ## SEE ALSO [meson-reference(3)](/meson-reference/3.md) [meson(1)](/meson/1.md) muon(1)