Pipe output directly to str and avoid additional memory allocations

Currently, there are lots of examples of code like this,
```
str << ('<tag ' << foo << ' ' << bar << '/>')
```
which create the string for the tag in memory before piping to str.

We can avoid creating all of these intermediate strings by dropping
the paranthesis and piping directly to str.

This relies on the `str` passed around to handle lots of small
appends. This is a problem when using RubyZip, but that is solved
in the next commit.

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/axlsx/drawing/graphic_frame.rb b/lib/axlsx/drawing/graphic_frame.rb
index 7d0e818c..4e5b4c36 100644
--- a/lib/axlsx/drawing/graphic_frame.rb
+++ b/lib/axlsx/drawing/graphic_frame.rb
@@ -35,7 +35,7 @@ module Axlsx
       # macro attribute should be optional!
       str << '<xdr:graphicFrame>'
       str << '<xdr:nvGraphicFramePr>'
-      str << (+'<xdr:cNvPr id="' << @anchor.drawing.index.to_s << '" name="' << 'item_' << @anchor.drawing.index.to_s << '"/>')
+      str << '<xdr:cNvPr id="' << @anchor.drawing.index.to_s << '" name="' << 'item_' << @anchor.drawing.index.to_s << '"/>'
       str << '<xdr:cNvGraphicFramePr/>'
       str << '</xdr:nvGraphicFramePr>'
       str << '<xdr:xfrm>'
@@ -43,8 +43,8 @@ module Axlsx
       str << '<a:ext cx="0" cy="0"/>'
       str << '</xdr:xfrm>'
       str << '<a:graphic>'
-      str << (+'<a:graphicData uri="' << XML_NS_C << '">')
-      str << (+'<c:chart xmlns:c="' << XML_NS_C << '" xmlns:r="' << XML_NS_R << '" r:id="' << rId << '"/>')
+      str << '<a:graphicData uri="' << XML_NS_C << '">'
+      str << '<c:chart xmlns:c="' << XML_NS_C << '" xmlns:r="' << XML_NS_R << '" r:id="' << rId << '"/>'
       str << '</a:graphicData>'
       str << '</a:graphic>'
       str << '</xdr:graphicFrame>'