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The Template Implementation

The C++ template(1) facility, which effectively allows use of variables for types in declarations, is one of the newest features of the language.

GNU C++ is one of the first compilers to implement many of the template facilities currently defined by the ANSI committee.

Nevertheless, the template implementation is not yet complete. This chapter maps the current limitations of the GNU C++ template implementation.

Limitations for function and class templates

These limitations apply to any use of templates (function templates or class templates) with GNU C++:

Template definitions must be visible
When you compile code with templates, the template definitions must come first (before the compiler needs to expand them), and template definitions you use must be visible in the current scope.
Individual initializers needed for static data
Templates for static data in template classes do not work. See section Limitations for class templates.

Limitations for function templates

Function templates are implemented for the most part. The compiler can correctly determine template parameter values, and will delay instantiation of a function that uses templates until the requisite type information is available.

The following limitations remain:

Limitations for class templates

Debugging information for templates

Debugging information for templates works for some object code formats, but not others. It works for stabs(2) (used primarily in A.OUT object code, but also in the Solaris 2 version of ELF), and the MIPS version of COFF debugging format.

DWARF support is currently minimal, and requires further development.

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