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18.13 命名空间</div>
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SystemVerilog has eight name spaces for identifiers, two are global (definitions name space and package name space), two are global to the compilation unit (compilation unit name space and text macro name space) and four are local. The eight name spaces are described as follows:
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<li value="1" class="Element606">The definitions name space unifies all the non-nested module, macromodule, primitive, program, and interface identifiers defined outside of all other declarations. Once a name is used to define a module, macromodule, primitive, program, or interface within one compilation unit the name shall not be used again (in any compilation unit) to declare another non-nested module, macromodule, primitive, program, or interface outside of all other declarations. This is compatible with the definitions name space as defined in IEEE 1364-2001.</li>
<li value="2" class="Element606">The package name space unifies all the package identifiers defined among all compilation units. Once a name is used to define a package within one compilation unit the name shall not be used again to declare another package within any compilation unit.</li>
<li value="3" class="Element606">The compilation-unit scope name space exists outside the module, macromodule, interface, package, program, and primitive constructs. It unifies the definitions of the functions, tasks, parameters, named events, net declarations, variable declarations and user defined types within the compilation-unit scope.</li>
<li value="4" class="Element606">The text macro name space is global within the compilation unit. Since text macro names are introduced and used with a leading ‘ character, they remain unambiguous with any other name space. The text macro names are defined in the linear order of appearance in the set of input files that make up the compilation unit. Subsequent definitions of the same name override the previous definitions for the balance of the input files.</li>
<li value="5" class="Element606">The module name space is introduced by the module, macromodule, interface, package, program, and primitive constructs. It unifies the definition of modules, macromodules, interfaces, programs, functions, tasks, named blocks, instance names, parameters, named events, net declarations, variable declarations and user defined types within the enclosing construct.</li>
<li value="6" class="Element606">The block name space is introduced by named or unnamed blocks, the specify, function, and task constructs. It unifies the definitions of the named blocks, functions, tasks, parameters, named events, variable type of declaration and user defined types within the enclosing construct.</li>
<li value="7" class="Element606">The port name space is introduced by the module, macromodule, interface, primitive, and program constructs. It provides a means of structurally defining connections between two objects that are in two different name spaces. The connection can be unidirectional (either input or output) or bidirectional (inout or ref). The port name space overlaps the module and the block name spaces. Essentially, the port name space specifies the type of connection between names in different name spaces. The port type of declarations includes input, output, inout, and ref. A port name introduced in the port name space can be reintroduced in the module name space by declaring a variable or a net with the same name as the port name.</li>
<li value="8" class="Element606">The attribute name space is enclosed by the (* and *) constructs attached to a language element (see Section 2.8). An attribute name can be defined and used only in the attribute name space. Any other type of name cannot be defined in this name space.</li>
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