Question

The code

string bar = "Hello ";
const(char) * foo = "world!";
bar ~= foo;

fails to compile in the third line. Why? What elegant alternatives do I have?

The error output is Error: cannot append type const(char)* to type string.

Answer 1

Don’t use a const(char)*?

string bar = "Hello ";
string foo = "world!";
bar ~= foo;

String literals in D are of type string, you shouldn’t ever need to use a const(char)*, except when interfacing with C code.

The reason D doesn’t allow that concatenation is because const(char)* isn’t a string, in any sense of the word. Strings in D are immutable(char)[] (which is alias‘d by string). A const(char)* is just a pointer to a constant character. Unlike C and C++, there is no implied null-terminator, so D can’t and won’t assume there is one.

If for whatever reason you absolutely must use a const(char)* and you know that it is null terminated, then you can make a const(char)[] out of it by slicing, which you can then append to a string:

string bar = "Hello ";
const(char)* foo = "world!";
bar ~= foo[0..strlen(foo)];