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Diffstat (limited to 'source/00_content/articles')
-rw-r--r-- | source/00_content/articles/2014-07-11_mapping_arrays_using_tuples_in_cpp11.md | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/source/00_content/articles/2014-07-11_mapping_arrays_using_tuples_in_cpp11.md b/source/00_content/articles/2014-07-11_mapping_arrays_using_tuples_in_cpp11.md index db55e00..99a8dce 100644 --- a/source/00_content/articles/2014-07-11_mapping_arrays_using_tuples_in_cpp11.md +++ b/source/00_content/articles/2014-07-11_mapping_arrays_using_tuples_in_cpp11.md @@ -2,7 +2,7 @@ During my proof-of-concept implementation of external functions enabling [XSLT based static site generation](https://github.com/KnairdA/InputXSLT) I came upon the problem of calling a template method specialized on the Nth type of a `std::tuple` specialization using the Nth element of a array-like type instance as input. This was needed to implement a generic template-based interface for implementing [Apache Xalan](http://xalan.apache.org/xalan-c/index.html) external functions. This article aims to explain the particular approach taken to solve this problem. -While it is possible to unpack a `std::tuple` instance into individual predefined objects using `std::tie` the standard library offers no such helper template for `unpacking` an array into individual objects and calling appropriate casting methods defined by a `std::tuple` mapping type. Sadly exactly this functionality is needed so that we are able to call a `constructDocument` member method of a class derived from the [`FunctionBase`](https://github.com/KnairdA/InputXSLT/blob/master/src/function/base.h) external function interface template class using static polymorphism provided through the [curiously recurring template pattern](https://en.wikipedia.org/wiki/Curiously_Recurring_Template_Pattern). This interface template accepts the desired external function arguments as variadic template types and aims to provide the required validation and conversion boilerplate implementation. While we could recursively generate a `std::tuple` specialization instance from an array-like type using a approach simmilar to the one detailed in my article on [mapping binary structures as tuples using template metaprogramming](http://blog.kummerlaender.eu/artikel/mapping-binary-structures-as-tuples-using-template-metaprogramming) this wouldn't solve the problem of passing on the resulting values as individual objects. This is why I had to take the new approach of directly calling a template method on individual array elements using a `std::tuple` specialization as a kind of blueprint and passing the result values of this method to the `constructDocument` method as separate arguments. +While it is possible to unpack a `std::tuple` instance into individual predefined objects using `std::tie` the standard library offers no such helper template for `unpacking` an array into individual objects and calling appropriate casting methods defined by a `std::tuple` mapping type. Sadly exactly this functionality is needed so that we are able to call a `constructDocument` member method of a class derived from the [`FunctionBase`](https://github.com/KnairdA/InputXSLT/blob/master/src/function/base.h) external function interface template class using static polymorphism provided through the [curiously recurring template pattern](https://en.wikipedia.org/wiki/Curiously_Recurring_Template_Pattern). This interface template accepts the desired external function arguments as variadic template types and aims to provide the required validation and conversion boilerplate implementation. While we could recursively generate a `std::tuple` specialization instance from an array-like type using a approach simmilar to the one detailed in my article on [mapping binary structures as tuples using template metaprogramming](/article/mapping_binary_structures_as_tuples_using_template_metaprogramming) this wouldn't solve the problem of passing on the resulting values as individual objects. This is why I had to take the new approach of directly calling a template method on individual array elements using a `std::tuple` specialization as a kind of blueprint and passing the result values of this method to the `constructDocument` method as separate arguments. Extracting array elements obviously requires some way of defining the appropriate indexes and mapping the elements using a tuple blueprint additionally requires this way to be statically resolvable as one can not pass a dynamic index value to `std::tuple_element`. So the first step to fullfilling the defined requirements involved the implementation of a template based index or sequence type. |