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12345678910111213141516171819202122232425262728293031323334353637383940414243#include <vector> class foo { public: class builder; foo(int prop1, bool prop2, bool prop3, std::vector<int> prop4) : prop1{prop1}, prop2{prop2}, prop3{prop3}, prop4{prop4} { } int prop1; bool prop2; bool prop3; std::vector<int> prop4; }; class foo::builder { public: builder& set_prop1(int value) { prop1 = value; return *this; }; builder& set_prop2(bool value) { prop2 = value; return *this; }; builder& set_prop3(bool value) { prop3 = value; return *this; }; builder& set_prop4(std::vector<int> value) { prop4 = value; return *this; }; foo build() const { return foo{prop1, prop2, prop3, prop4}; } private: int prop1 = 0; bool prop2 = false; bool prop3 = false; std::vector<int> prop4 = {}; }; int main() { foo f = foo::builder{}.set_prop1(5) .set_prop3(true) .build(); }

This sample is licensed under the CC0 Public Domain Dedication.


Separate the complex construction of an object from its representation.


The foo class, on lines 3–16, has a complex construction process during which any subset of its properties might be set. This process is captured by the foo::builder class, on lines 18–36. This builder class provides an interface for constructing foo objects, allowing various combinations of parameters to be provided. This avoids having to define a large collection of constructors for foo.

The foo::builder class implements a set of chainable functions for setting the construction parameters (lines 21–24) and a build member function for constructing the foo object with these parameters (lines 26–29).

On lines 40–42, we use foo::builder to construct a foo object, setting its prop1 and prop3 members and calling build to construct the object.


  • Joseph Mansfield

Last Updated

04 April 2015


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