On Mon, Dec 30, 2019 at 03:31:31PM -0800, H. S. Teoh via Digitalmars-d-learn wrote: > On Mon, Dec 30, 2019 at 03:09:58PM -0800, H. S. Teoh via Digitalmars-d-learn > wrote: > [...] > > I suspect the cause is that whatever Grapheme.opSlice returns is > > going out-of-scope when used with .map, that's why it's > > malfunctioning. > [...] > > Haha, it's actually right there in the Grapheme docs for the opSlice > overloads: > > Random-access range over Grapheme's $(CHARACTERS). > > Warning: Invalidates when this Grapheme leaves the scope, > attempts to use it then would lead to memory corruption. > > Looks like when you use .map over the Grapheme, it gets copied into a > temporary, which gets invalidated when map.front returns. Somewhere > we're missing a 'scope' qualifier... [...]
Indeed, compiling with dmd -dip1000 produces this error message: test.d(15): Error: returning g.opSlice() escapes a reference to parameter g, perhaps annotate with return /usr/src/d/phobos/std/algorithm/iteration.d(499): instantiated from here: MapResult!(__lambda1, Grapheme) test.d(15): instantiated from here: map!(Grapheme) Not the most helpful message (the annotation has to go in Phobos code, not in user code), but it does at least point to the cause of the problem. T -- What doesn't kill me makes me stranger.