On 28.09.2016 22:16, Walter Bright wrote:
On 9/28/2016 6:58 AM, Timon Gehr wrote:
An excellent example of that is the std.regex package.
It's actually a bad example, because it is irrelevant: it is obviously
a bad
idea to implement regex using operator overloading, because the regex
operators
have no D equivalent.
Yet this "obviously bad" idea regularly resurfaces as a cool use of
expression templates and respected people in the industry like it and
advocate it.
...
This is not surprising. C++ has no good options.
Assume I have two symbolic expressions a and b:
Expression a=variable("a"), b=variable("b");
Why should I be allowed to do
auto c = a + b; // symbolic value a + b
but not
auto d = a <= b; // symbolic value a <= b
Because there is no way to stop the former but still have operator
overloading.
...
What's wrong with that usage? (This is NOT expression templates.)
The string parsing approach is not useful here: how do I use existing
expressions that are accessible in the scope to build new expressions?
You seem to be asking for expression templates.
No. It's symbolic computation at run time. Think Wolfram Mathematica.
