effective java builder idiom equivalent in c++?
This is a great idiom I've been using since reading Effective Java. I've been trying to find a C++ equivalent or something similar and have had lit开发者_开发技巧tle luck. The traditional builder pattern found in the GoF book isn't really applicable in my case. It's one complicated object that has a very messy constructor. Below is a small implementation of the Java.
class ComplicatedObject {
private String field1;
private String field2;
private int field3;
private ComplicatedObject(Builder builder) {
this.field1 = builder.myField1;
this.field2 = builder.myField2;
this.field3 = builder.myField3;
}
public static class Builder {
private String myField1 = "some default";
private String myField2 = "some other default";
private int myField3 = -1;
public Builder() { }
public Builder field1(String val) {
this.myField1 = val;
return this;
}
public Builder field2(String val) {
this.myField2 = val;
return this;
}
public Builder field3(int val) {
this.myField3 = val;
return this;
}
public ComplicatedObject build() {
return new ComplicatedObject(this);
}
}
public static void main(final String[] args) {
//built like this
ComplicatedObject obj = new ComplicatedObject.Builder().field1("blah").field2("lol").field3(4).build();
}
}
Not only can it be adapted to C++ but rather the idiom has been adapted from C++.
I think the first time I heard of this idiom was before Java came into existence. IIRC Bjarne Stroustrup mentions this in C++ 2nd Edition as an explanation of why C++ does not need Smalltalk style named parameters.
I could have my dates wrong but this is about 15 years old in C++.
EDIT: It seems it wad first described in Design and Evolution of C++ (6.5.1) where it was called named function parameters
#include <iostream>
#include <string>
using namespace std;
class ComplicatedObject {
public: class Builder {
friend class ComplicatedObject;
private: string myField1;
private: string myField2;
private: int myField3;
public: Builder()
: myField1("some default"),
myField2 ("some other default"),
myField3(-1)
{ }
public: Builder& field1(const string& val) {
myField1 = val;
return *this;
}
public: Builder& field2(const string& val) {
myField2 = val;
return *this;
}
public: Builder& field3(int val) {
myField3 = val;
return *this;
}
public: ComplicatedObject build() {
return ComplicatedObject(*this);
}
};
private: string field1;
private: string field2;
private: int field3;
private: ComplicatedObject(const Builder& builder)
:field1(builder.myField1),
field2(builder.myField2),
field3(builder.myField3)
{}
};
int main(int argc, char** argv) {
if (argc < 4) {
std::cout << "not enough params.";
return 1;
}
ComplicatedObject obj(ComplicatedObject::Builder().field1("blah").field2("lol").field3(4));
}
I made minimal changes to make it C++, fast, and safe. http://ideone.com/sCH1V
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