Bug 17623 – Unexpected failure of an assertion on empty strings

According to the documentation [1]: "For static and dynamic arrays, identity is defined as referring to the same array elements and the same number of elements." this code $ cat stringidentity.d void main () { string s = null; string t = ""; assert (s is t); } shall pass but the assertion fails $ ./stringidentity [email protected](5): Assertion failure [1] https://dlang.org/spec/expression.html#identity_expressions

This is a documentation bug; the code is correct. A dynamic array in D is represented as a pointer (.ptr) and a length (.length). > string s = null; s.length is 0 and s.ptr is null. > string t = ""; t.length is also 0, but t.ptr points towards a zero-length string literal. The distinction is mainly that D string literals are zero-terminated, so that they can be implicitly converted to a C string (const char*).

(In reply to Vladimir Panteleev from comment #1) > The distinction is mainly that D string literals are zero-terminated, so > that they can be implicitly converted to a C string (const char*). The nonidentity of null and "" arises from null not having a NUL "at the end"?

The documentation is not wrong. To me this looks like quirk involving dynamic arrays and string literals. Although it is not specifically spelled out, the spec [1] does document string literals as being 0 terminated. So I think that this issue is invalid. [1] https://dlang.org/spec/arrays.html#printf

(In reply to RazvanN from comment #3) > The documentation is not wrong. That is an untrue statement. The documentation /is/ wrong [1]. Both s and t in string s = null; string t = ""; refer to the same elements and have the same number of elements. The documentation must be corrected. A possible replacement for the original statement For static and dynamic arrays, identity is defined as referring to the same array elements and the same number of elements. is For static and dynamic arrays, identity of two arrays is given when both arrays refer to the same memory location and contain the same number of elements. [1] http://forum.dlang.org/post/[email protected]

@RazvanN7 created dlang/dlang.org pull request #3345 "Fix Issue 17623 - Unexpected failure of an assertion on empty strings" fixing this issue: - Fix Issue 17623 - Unexpected failure of an assertion on empty strings https://github.com/dlang/dlang.org/pull/3345

dlang/dlang.org pull request #3345 "Fix Issue 17623 - Unexpected failure of an assertion on empty strings" was merged into master: - 7c45b3aae88e23c10ed2a292e70d85fd3db0221a by Razvan Nitu: Fix Issue 17623 - Unexpected failure of an assertion on empty strings https://github.com/dlang/dlang.org/pull/3345