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Editorial Team
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Asked: 2026-06-18T17:44:21+00:00

The following class template Sequencer contains a nested class template Process , with two

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The following class template Sequencer contains a nested class template Process, with two template arguments.

template<typename P>
struct Sequencer
{   
    template<typename A , bool = A::CAN_BE_BUFFERED>
    struct Process;
};

I would like to specialize Sequencer for a custom struct Foo while specializing its own version of Process to support just one template argument as follows

template<>
struct Sequencer<Bar>
{   
    template<typename A>
    struct Process;
};

As the implementation is too long, I’ve posted the entire listing on ideone.

On GCC 4.5.3 I get the following error message

prog.cpp:60:24: error: partial specialization ‘Sequencer<Bar>::Process<A>’ does not specialize any template arguments

On Visual Studio 2008 I get the following error

prog.cpp(62) : error C2753: 'Sequencer<Bar>::Process<A>' : partial specialization cannot match argument list for primary template
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1 Answer

  1. Editorial Team

    Sequencer<Bar>::Process is a full template, it is not a specialization. It just happens to be a member of a specialization. You shouldn’t be declaring it as a specialization:

    template<typename A>
struct Sequencer<Bar>::Process/*<A>*/
                               //^ remove this
{
};

    Templates should be thought of as “class generators”. Sequencer<P> defines a way to make classes from an arbitrary P, where Sequencer<Bar> gives a particular class to generate when Sequencer<Bar> is instantiated. Each generated class is totally separated and unrelated (beyond having been created by the same generator). In this case, this means that the inner class in Sequencer<Bar> has no relationship with the inner class in Sequencer<P>.

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