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A Variadic Sequence is a member of a family of sequence classes with both variadic and numbered forms. If seq is a generic name for some Variadic Sequence, its variadic form allows us to specify a sequence of n elements t1,t2,... tn, for any n from 0 up to a preprocessor-configurable limit BOOST_MPL_LIMIT_seq_SIZE, using the following notation:
seq<t1,t2,... tn>
By contrast, each numbered sequence form accepts the exact number of elements that is encoded in the name of the corresponding class template:
seqn<t1,t2,... tn>
For numbered forms, there is no predefined top limit for n, aside from compiler limitations on the number of template parameters.
In the following table and subsequent specifications, seq is a placeholder token for the actual Variadic Sequence name.
| Expression | Type | Complexity |
|---|---|---|
| seq<t1,t2,... tn> | Forward Sequence | Amortized constant time |
| seq<t1,t2,... tn>::type | Forward Sequence | Amortized constant time |
| seqn<t1,t2,... tn> | Forward Sequence | Amortized constant time |
| seqn<t1,t2,... tn>::type | Forward Sequence | Amortized constant time |
typedef seq<t1,t2,... tn> s; typedef seqn<t1,t2,... tn> s;
| Semantics: | s is a sequence of elements t1,t2,... tn. |
|---|---|
| Postcondition: | size<s>::value == n. |
typedef seq<t1,t2,... tn>::type s; typedef seqn<t1,t2,... tn>::type s;
| Semantics: | s is identical to seqn<t1,t2,... tn >. |
|---|---|
| Postcondition: | size<s>::value == n. |