add sizehint(Vector, sz). fixes #2230

base/array.jl

@@ -675,6 +675,11 @@ function resize!(a::Vector, nl::Integer)
     return a
 end
 
+function sizehint(a::Vector, sz::Integer)
+    ccall(:jl_array_sizehint, Void, (Any, Uint), a, sz)
+    a
+end
+
 function pop!(a::Vector)
     if isempty(a)
         error("pop!: array is empty")

base/intset.jl

@@ -23,7 +23,7 @@ function sizehint(s::IntSet, top::Integer)
         end
         s.limit = top
     end
-    s.limit
+    s
 end
 
 function add!(s::IntSet, n::Integer)

src/array.c

@@ -502,6 +502,15 @@ void jl_array_del_end(jl_array_t *a, size_t dec)
     a->length -= dec; a->nrows -= dec;
 }
 
+void jl_array_sizehint(jl_array_t *a, size_t sz)
+{
+    if (sz <= jl_array_len(a))
+        return;
+    size_t inc = sz - jl_array_len(a);
+    jl_array_grow_end(a, inc);
+    a->length -= inc; a->nrows -= inc;
+}
+
 void jl_array_grow_beg(jl_array_t *a, size_t inc)
 {
     // designed to handle the case of growing and shrinking at both ends

src/julia.expmap

@@ -53,6 +53,7 @@
     jl_array_del_end;
     jl_array_grow_beg;
     jl_array_grow_end;
+    jl_array_sizehint;
     jl_array_ptr;
     jl_arrayref;
     jl_arrayset;

src/julia.h

@@ -754,6 +754,7 @@ DLLEXPORT void jl_array_grow_end(jl_array_t *a, size_t inc);
 DLLEXPORT void jl_array_del_end(jl_array_t *a, size_t dec);
 DLLEXPORT void jl_array_grow_beg(jl_array_t *a, size_t inc);
 DLLEXPORT void jl_array_del_beg(jl_array_t *a, size_t dec);
+DLLEXPORT void jl_array_sizehint(jl_array_t *a, size_t sz);
 DLLEXPORT void *jl_value_ptr(jl_value_t *a);
 void jl_cell_1d_push(jl_array_t *a, jl_value_t *item);