Bug 5198 – Appender much slower when appending ranges of elements than individual elements

Given an appender Appender!string a, the following code should be roughly equivalent performance-wise: a.put(' '); a.put(" "); But as shown by this code, the version that puts an individual character is an order of magnitude faster. import std.stdio; import std.date; import std.array; void f0() { Appender!string a; a.reserve(100_000_000); foreach(i; 0 .. 100_000_000) { a.put(' '); } } void f1() { Appender!string a; a.reserve(100_000_000); foreach(i; 0 .. 100_000_000) { a.put(" "); } } void main() { auto r = benchmark!(f0)(1); writeln(r, "ms"); r = benchmark!(f1)(1); writeln(r, "ms"); } Results: [2433]ms [13276]ms Swapping the order of testing does not change the situation.

Great catch! I'm marking this as "assigned" as I see you've already assign it to yourself. Long term I wonder whether we should include performance tests as part of build acceptance tests.

turns out the appender was not reserving any extra space when appending an array, it was simply reallocating -- just enough to hold the existing data + the new data (in this example, 1 more element). I fixed it so the same algorithm used to expand the array for one element is now used to append an array of elements. changeset http://www.dsource.org/projects/phobos/changeset/2237