C++11 simple lambda predicate syntax sample

I have done a simple sample how to use a C++11 lambda expression as predicate for a particular algorithm.

	#include <iostream>
	#include <string>
	#include <algorithm>
	int main() {
	std::string s = "xAAAyyByABCxGxZyIxGyyZI";
	std::cout << "Before: '" << s << "'" << std::endl;
	bool (*pred1)(char) = [](char c) { return c == 'x' || c == 'y'; };
	std::replace_if(s.begin(),s.end(),pred1,'*');
	std::cout << "1st tr: '" << s << "'" << std::endl;
	auto pred2 = [](char c) { return c == '*'; };
	std::replace_if(s.begin(),s.end(),pred2,'#');
	std::cout << "2nd tr: '" << s << "'" << std::endl;
	return 0;
	}

view raw PredicateLambda.cpp hosted with ❤ by GitHub

pred1 demonstrates the result type of a lambda expression is a function pointer.
pred2 demonstrates how to shorten the lengthy type declaration.

Conditional type selection using C++ template specializations

One of the very basic techniques of C++ meta-programming is to provide simple selector classes that provide to refer to a type from a (public) typedef member.

The basic pattern for type selections based on a condition applied to the template parameters passed, or even independently looks like the following code demonstrates:

---

	#include <iostream>
	#include <typeinfo>
	using namespace std;
	template<typename FalseType, typename TrueType, bool condition>
	struct ConditionalTypeSelector
	{
	typedef void ResultType;
	};
	template<typename FalseType, typename TrueType>
	struct ConditionalTypeSelector<FalseType,TrueType,false>
	{
	typedef FalseType ResultType;
	};
	template<typename FalseType, typename TrueType>
	struct ConditionalTypeSelector<FalseType,TrueType,true>
	{
	typedef TrueType ResultType;
	};
	struct A {
	unsigned char member;
	};
	struct B {
	int member;
	};
	struct C {
	long long member;
	};
	int main() {
	cout << typeid
	( ConditionalTypeSelector
	< A,B,(sizeof(A) > sizeof(B))
	>::ResultType
	).name() << endl;
	cout << typeid
	( ConditionalTypeSelector
	< A,B,(sizeof(B) > sizeof(A))
	>::ResultType
	).name() << endl;
	cout << typeid
	( ConditionalTypeSelector
	< A,C,(sizeof(A) > sizeof(C))
	>::ResultType
	).name() << endl;
	cout << typeid
	( ConditionalTypeSelector
	< C,B,true>::ResultType
	).name() << endl;
	cout << typeid
	( ConditionalTypeSelector
	< C,A,false>::ResultType
	).name() << endl;
	return 0;
	}

view raw ConditionalTypeSelectorSample.cpp hosted with ❤ by GitHub

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A compiled and running example of the above code can be found here.