定义并返回一个函数的功能? [英] Define and return a function from a function?
问题描述
例如,我们有一个函数,如:
float foo(float val){return val * val;}
现在需要的是像bar这样的函数:
$ $ $ $ $ $ $ $ typedef float(* func_t)(float)
//擦亮伪代码
func_t bar(float coeff){return coeff * foo();}
//真实意图,创建一个返回foo变体的函数
/ /乘以coeff。 h(x)= coeff * foo(x)
远在使用lambda或类。有没有一种简单的方法可以做到这一点,而不会毫无必要地变得复杂? 解决方案
闭包(使用 std :: function
) - 使用 lambda函数 - 在C ++ 11中是合适的,并在这里推荐。所以有
std :: function< int(int)> translate(int delta){
return [delta](int x){return x + delta;}}
然后你可能会后来编码:
auto t3 = translate(3);
现在 t3
是函数后来增加3:
int y = t3(2),z = t3(5);
当然有 y
5并且 z
为8。
您也可以使用 JIT编译库,以实时生成机器码,例如 GCCJIT 或 LLVM 或 libjit 或 asmjit ;或者你甚至可以在一些生成的文件 /tmp/mygencod.cc
中生成一些C ++(或C)代码,并为其编译(例如 g ++ -Wall -O -fPIC /tmp/mygencod.cc -shared -o /tmp/mygencod.so
)转换为 /tmp/mygencod.so
插件然后动态加载该插件使用 dlopen
在POSIX系统上(以及后来的 dlsym 从名称中获取函数指针;注意名称对C ++进行修复)。我在 GCC MELT 中进行此类操作
How does one define and return a function inside a function?
For instance, we have a function like:
float foo(float val) {return val * val;}
Now, what is needed is a function like bar:
typedef float (*func_t)(float)
// Rubish pseudo code
func_t bar(float coeff) {return coeff * foo();}
// Real intention, create a function that returns a variant of foo
// that is multiplied by coeff. h(x) = coeff * foo(x)
The only thing I've came up with so far is using lambda or a class. Is there a straight forward way to do this without being convoluted needlessly?
Closures (with std::function
) -using lambda functions- in C++11 are appropriate and recommended here. So have
std::function<int(int)> translate (int delta) {
return [delta](int x) {return x+delta;} }
then you might later code:
auto t3 = translate(3);
Now t3
is the "function" which adds 3, later:
int y = t3(2), z = t3(5);
and of course have y
be 5 and z
be 8.
You could also use some JIT compilation library to generate machine code on the fly, e.g. GCCJIT, or LLVM or libjit, or asmjit; or you could even generate some C++ (or C) code in some generated file /tmp/mygencod.cc
and fork a compilation of that (e.g. g++ -Wall -O -fPIC /tmp/mygencod.cc -shared -o /tmp/mygencod.so
) into a /tmp/mygencod.so
plugin then dynamically load that plugin using dlopen
on POSIX systems (and later dlsym to get a function pointer from a name; beware of name mangling for C++). I am doing such things in GCC MELT
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