Lambda Expressions in C++
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The document discusses lambda expressions in C++, including their syntax and usage in functional programming. It covers important concepts such as capturing variables, initializing captures with C++14, and applying functions for dependency injection. Various examples are provided to illustrate the practical applications of lambdas in algorithms and data manipulation.
![[](){}();
Or How I Learned To Stop Worrying and Love the
Lambda
Pat Viafore
HSV.cpp Meetup
3/15/2017](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-1-320.jpg)
![[](){}](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-6-320.jpg)
![[](){}](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-7-320.jpg)
![[](){}
Function
Body](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-8-320.jpg)
![void print(std::function<bool()> func)
{
std::string str = func() ? "true" : "false";
std::cout << str << “n”;
}
auto isFiveGreaterThanThree = [](){ return 5 > 3; };
print(isFiveGreaterThanThree);](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-9-320.jpg)
![[](){}
Parameters
Function
Body](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-10-320.jpg)
{ return num > 3; };
print(5, isGreaterThanThree);](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-11-320.jpg)
![[](){}
Capture
List
Parameters
Function
Body](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-12-320.jpg)
{ return n > target; };
target = 6;
print(5, isGreaterThan);](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-13-320.jpg)
![Capture List
By Value By Reference
[this]
[a,b]
[=]
[&a,&b]
[&]
Prefer Explicit Captures Over
Default Captures](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-14-320.jpg)
![class A {
public:
int x;
A(): x(10) {}
std::function<bool()> getLambda()
{
return [=](){ return x+2; };
}
};
int main()
{
A* a = new A();
auto lambda = a->getLambda();
delete a;
lambda();
}
This is implicitly this->x. The this
parameter is what gets captured, not
x.](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-15-320.jpg)
![class A {
public:
int x;
A(): x(10) {}
std::function<bool()> getLambda()
{
return [copy=x](){ return copy+2; };
}
};
int main()
{
A* a = new A();
auto lambda = a->getLambda();
delete a;
lambda();
}
C++14 gives us init captures,
where we can initialize the
variables we capture (useful for
any non-local captures)](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-16-320.jpg)
{ return MacAddress::ItuAddress == mac; };
any_of(macs.begin(), macs.end(), isSpecial);
count_if(macs.begin(), macs.end(), isSpecial);
replace_if(macs.begin(), macs.end(), isSpecial, MacAddress::BlankMacAddress);
sort(ips.begin(), ips.end(), [](IpAddressV4& ip1, IpAddressV4& ip2)
{ return ip1.getNetworkByteOrder() < ip2.getNetworkByteOrder()); });](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-17-320.jpg)
![[](){}
Capture
List
Parameters
Function
Body
();](https://image.slidesharecdn.com/gjsgfk7driusun4ldthp-signature-02617a129911388d5f11d58adf2ac80095d9d5e389ad1a143f91e134e2b5c310-poli-170316125924/85/Lambda-Expressions-in-C-18-320.jpg)
Lambda Expressions in C++
- 1. [](){}(); Or How I Learned To Stop Worrying and Love the Lambda Pat Viafore HSV.cpp Meetup 3/15/2017
- 3. Lambda Expressions Lambda Calculus Church-Turing Thesis Conversion and Reduction Complicated Mathematics Functional Programming Underpinnings of Computer Science Lisp?
- 6. [](){}
- 7. [](){}
- 9. void print(std::function<bool()> func) { std::string str = func() ? "true" : "false"; std::cout << str << “n”; } auto isFiveGreaterThanThree = [](){ return 5 > 3; }; print(isFiveGreaterThanThree);
- 11. void print(int param, std::function<bool(int)> func) { std::string str = func(param) ? "true" : "false"; std::cout << str << “n”; } auto isGreaterThanThree = [](int num){ return num > 3; }; print(5, isGreaterThanThree);
- 13. void print(int num, std::function<bool(int)> func) { std::string str = func(num) ? "true" : "false"; std::cout << str << “n”; } int target = 3; auto isGreaterThan = [target](int n){ return n > target; }; target = 6; print(5, isGreaterThan);
- 14. Capture List By Value By Reference [this] [a,b] [=] [&a,&b] [&] Prefer Explicit Captures Over Default Captures
- 15. class A { public: int x; A(): x(10) {} std::function<bool()> getLambda() { return [=](){ return x+2; }; } }; int main() { A* a = new A(); auto lambda = a->getLambda(); delete a; lambda(); } This is implicitly this->x. The this parameter is what gets captured, not x.
- 16. class A { public: int x; A(): x(10) {} std::function<bool()> getLambda() { return [copy=x](){ return copy+2; }; } }; int main() { A* a = new A(); auto lambda = a->getLambda(); delete a; lambda(); } C++14 gives us init captures, where we can initialize the variables we capture (useful for any non-local captures)
- 17. Why? Dependency Injection Pass a function to inject a dependency Functional Programming Styles Mapping and Filtering just got a whole lot easier Algorithm Library auto isSpecial = [](MacAddress& mac){ return MacAddress::ItuAddress == mac; }; any_of(macs.begin(), macs.end(), isSpecial); count_if(macs.begin(), macs.end(), isSpecial); replace_if(macs.begin(), macs.end(), isSpecial, MacAddress::BlankMacAddress); sort(ips.begin(), ips.end(), [](IpAddressV4& ip1, IpAddressV4& ip2) { return ip1.getNetworkByteOrder() < ip2.getNetworkByteOrder()); });