Modules
Module: ModuleDeclaration DeclDefs DeclDefs DeclDefs: DeclDef DeclDef DeclDefs DeclDef: AttributeSpecifier ImportDeclaration EnumDeclaration ClassDeclaration InterfaceDeclaration AggregateDeclaration Declaration Constructor Destructor Invariant UnitTest StaticConstructor StaticDestructor DebugSpecification VersionSpecification ;Modules have a one-to-one correspondence with source files. The module name is the file name with the path and extension stripped off.
Modules automatically provide a namespace scope for their contents. Modules superficially resemble classes, but differ in that:
- There's only one instance of each module, and it is statically allocated.
- There is no virtual table.
- Modules do not inherit, they have no super modules, etc.
- Only one module per file.
- Module symbols can be imported.
- Modules are always compiled at global scope, and are unaffected by surrounding attributes or other modifiers.
Module Declaration
The ModuleDeclaration sets the name of the module and what package it belongs to. If absent, the module name is taken to be the same name (stripped of path and extension) of the source file name.ModuleDeclaration: module ModuleName ; ModuleName: Identifier ModuleName . IdentifierThe Identifier preceding the rightmost are the packages that the module is in. The packages correspond to directory names in the source file path.
If present, the ModuleDeclaration appears syntactically first in the source file, and there can be only one per source file.
Example:
module c.stdio; // this is module <b>stdio</b> in the <b>c</b> packageBy convention, package and module names are all lower case. This is because those names have a one-to-one correspondence with the operating system's directory and file names, and many file systems are not case sensitive. All lower case package and module names will minimize problems moving projects between dissimilar file systems.
Import Declaration
Rather than text include files, D imports symbols symbolically with the import declaration:ImportDeclaration: import ModuleNameList ; ModuleNameList: ModuleName ModuleName , ModuleNameListThe rightmost Identifier becomes the module name. The top level scope in the module is merged with the current scope.
Example:
import std.c.stdio; // import module <b>stdio</b> from the <b>c</b> package import foo, bar; // import modules <b>foo</b> and <b>bar</b>
Scope and Modules
Each module forms its own namespace. When a module is imported into another module, by default all its top level declarations are available without qualification. Ambiguities are illegal, and can be resolved by explicitly qualifying the symbol with the module name.For example, assume the following modules:
// Module foo int x = 1; int y = 2; // Module bar int y = 3; int z = 4;then:
import foo; ... q = y; // sets q to foo.yand:
import foo; int y = 5; q = y; // local y overrides foo.yand:
import foo; import bar; q = y; // error: foo.y or bar.y?and:
import foo; import bar; q = bar.y; // q set to 3If the import is private, such as:
module abc; private import def;then def is not searched when another module imports abc.
Module Scope Operator
Sometimes, it's necessary to override the usual lexical scoping rules to access a name hidden by a local name. This is done with the global scope operator, which is a leading '.':int x; int foo(int x) { if (y) return x; // returns foo.x, not global x else return .x; // returns global x }The leading '.' means look up the name at the module scope level.
Static Construction and Destruction
Static constructors are code that gets executed to initialize a module or a class before the main() function gets called. Static destructors are code that gets executed after the main() function returns, and are normally used for releasing system resources.Order of Static Construction
The order of static initialization is implicitly determined by the import declarations in each module. Each module is assumed to depend on any imported modules being statically constructed first. Other than following that rule, there is no imposed order on executing the module static constructors.Cycles (circular dependencies) in the import declarations are allowed as long as not both of the modules contain static constructors or static destructors. Violation of this rule will result in a runtime exception.