[英]c++ compile-time check function arguments
I'm searching a way to check function arguments in compile-time if it's possible to do for compiler. 如果可以为编译器做的话,我正在寻找一种在编译时检查函数参数的方法。
To be more specific: assume that we have some class Matrix. 更具体一点:假设我们有一些类Matrix。
class Matrix
{
int x_size;
int y_size;
public:
Matrix(int width, int height):
x_size{width},
y_size{height}
{}
Matrix():
Matrix(0, 0)
{}
};
int main()
{
Matrix a; // good.
Matrix b(1, 10); // good.
Matrix c(0, 4); // bad, I want compilation error here.
}
So, can I check or differentiate behavior (function overloading?) in case of static (source-encoded) values passed to function? 那么,在传递给函数的静态(源编码)值的情况下,我可以检查或区分行为(函数重载?)?
If value isn't static: 如果值不是静态的:
std::cin >> size;
Matrix d(size, size);
we're only able to do runtime checks. 我们只能做运行时检查。 But if values are encoded in source? 但是如果值在源代码中编码? Can I make compile-time check in this case? 在这种情况下我可以进行编译时检查吗?
EDIT: I think this can be possible with constexpr constructor , but anyway overloading with and without constexpr isn't allowed. 编辑:我认为这可以通过constexpr构造函数实现 ,但无论如何都不允许使用和不使用constexpr进行重载。 So problem can't be resolved in way I suppose. 所以问题无法以我想象的方式解决。
To get a compile time error you would need a template: 要获得编译时错误,您需要一个模板:
template <int width, int height>
class MatrixTemplate : public Matrix
{
static_assert(0 < width, "Invalid Width");
static_assert(0 < height, "Invalid Height");
public:
MatrixTemplate()
: Matrix(width, height)
{}
};
(Btw.: I suggest unsigned types for indices) (顺便说一句:我建议索引的无符号类型)
If you do not have static_assert (here I switch to unsigned): 如果你没有static_assert(这里我切换到unsigned):
template <unsigned width, unsigned height>
class MatrixTemplate : public Matrix
{
public:
MatrixTemplate()
: Matrix(width, height)
{}
};
template <> class MatrixTemplate<0, 0> {};
template <unsigned height> class MatrixTemplate<0, height> {};
template <unsigned width> class MatrixTemplate<width, 0> {};
There is no support for empty matrices (MatrixTemplate<0, 0>), here. 这里不支持空矩阵(MatrixTemplate <0,0>)。 But it should be an easy task to adjust the static_asserts or class MatrixTemplate<0. 但是调整static_asserts或类MatrixTemplate <0应该是一件容易的事。 0>. 0>。
You may add a method like this: 您可以添加如下方法:
template <int WIDTH, int HEIGHT>
Matrix CreateMatrix()
{
static_assert(WIDTH > 0, "WIDTH > 0 failed");
static_assert(HEIGHT > 0, "HEIGHT > 0 failed");
return Matrix(WIDTH, HEIGHT);
}
int main() {
Matrix m(0, 2); // no static check
Matrix m2 = CreateMatrix<0,2>(); // static check
return 0;
}
The way that linear algebra packages tend to do this is to use templates for fixed size matrices, as in: 线性代数包倾向于这样做的方式是使用固定大小矩阵的模板,如:
template<int x, int y> class Matrix { ... }
and an extra class for matrices that can change size at runtime 和一个可以在运行时改变大小的矩阵的额外类
class DynamicMatrix {...}
You still have to rely on the programmer actually using the first option when they want fixed size matrices, but the template version makes it easy to generate a compiler error when x
or y
are zero. 当他们想要固定大小的矩阵时,您仍然必须依赖程序员实际使用第一个选项,但是当x
或y
为零时,模板版本可以很容易地生成编译器错误。
Run-time: 运行:
Matrix(int width, int height):
x_size{width},
y_size{height}
{
assert(x_size>0);
assert(y_size>0);
}
Compile-time (Actually you couldn't do it with function arguments. You can use template ways): 编译时(实际上你无法使用函数参数。你可以使用模板方式):
template <size_t WIDTH, size_t HEIGHT>
class Matrix
{
const size_t x_size = WIDTH;
const size_t y_size = HEIGHT;
static_assert(WIDTH > 0, "Width must > 0");
static_assert(HEIGHT > 0, "Height must > 0");
};
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