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Artifact ID:	357b8bb0447778ca905097f1f8361c0e52f5f45db418780a22ead9b16383d7d3
Page Name:	string type conversions
Date:	2021-10-12 10:21:37
Original User:	admin
Parent:	60c3d80c7b01da575938a070c6f8c1bcf2075c5964e50c40ad4687e7102d23ce (diff)

string type conversions

Legend:

• copy - get a freshly allocated copy of the data (possibly in a different format, i.e. not bit-for-bit the same)
• alias - get a slice of the exact same data, without allocation
• dstring - read "dstring (or wstring)". Only big difference is that wstring has its own C string type with std.utf.toUTF16z

from string (or char[])

• string -> string: copy with st.idup or std.utf.toUTF8(st)
• string -> dstring: copy with std.utf.toUTF32(st) or std.conv.to!dstring(st)
• dstring -> string: copy with std.utf.toUTF8(st) or std.conv.to!string(st)
• string -> char[]: mutable copy with st.dup
• string -> immutable(ubyte)[]: alias with std.string.representation(st)
• string -> C string: copy with std.string.toStringz(st)
• char[] -> string: unsafe alias with std.exception.assumeUnique(st)

from "string literal"

• string literal -> C string: alias by using it where a C string is wanted, const(char)* s = "string literal", puts("hi")
• string -> C string: if a string definitely came from a string literal, then alias it with &st[0] (@safe doesn't like st.ptr which can be null)

from ubyte[]

• ubyte[] -> char[]: alias with std.string.assumeUTF(st). asserts on invalid UTF in debug builds
• ubyte[] -> char[]: alias with cast(char[]) st. still @safe when qualifiers (like const) aren't discarded

from C string

• C string -> string: unsafe alias with std.string.fromStringz(st)

from char range

• dchar range -> dstring: copy with std.array.array(st)
• dchar range -> dchar[]: copy with std.array.array(st)
• char range -> string: same as above, but with autodecoding you'll easily get dchar where you expected char. Suppress that with std.utf.byCodeUnit, e.g. string st = "hello".byCodeUnit.map!(c => c).array, which would normally require dstring st = ...

on mutability

• read D Spec - Type Qualifiers
• immutable(T)[] -> const(T)[]: implicit conversion
• immutable(T)* -> const(T)*: implicit conversion
• string -> char[]: st.dup
• string -> char*: cast(char*) std.string.toStringz(st) (not @safe, but safe as toStringz always copies)

basics/string_type_conversions.d covers this in greater detail, with unit tests. basics/unicode_ops.d may also be of interest.