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.

2 files changed, 6 insertions, 6 deletions

diff --git a/lib/axlsx/doc_props/app.rb b/lib/axlsx/doc_props/app.rb
index 3eae1e28..40a8184d 100644
--- a/lib/axlsx/doc_props/app.rb
+++ b/lib/axlsx/doc_props/app.rb
@@ -221,7 +221,7 @@ module Axlsx
     # @return [String]
     def to_xml_string(str = +'')
       str << '<?xml version="1.0" encoding="UTF-8"?>'
-      str << (+'<Properties xmlns="' << APP_NS << '" xmlns:vt="' << APP_NS_VT << '">')
+      str << '<Properties xmlns="' << APP_NS << '" xmlns:vt="' << APP_NS_VT << '">'
       Axlsx.instance_values_for(self).each do |key, value|
         node_name = Axlsx.camel(key)
         str << "<#{node_name}>#{value}</#{node_name}>"
diff --git a/lib/axlsx/doc_props/core.rb b/lib/axlsx/doc_props/core.rb
index 8d3292e9..8dbe4cf4 100644
--- a/lib/axlsx/doc_props/core.rb
+++ b/lib/axlsx/doc_props/core.rb
@@ -24,11 +24,11 @@ module Axlsx
     # @return [String]
     def to_xml_string(str = +'')
       str << '<?xml version="1.0" encoding="UTF-8"?>'
-      str << (+'<cp:coreProperties xmlns:cp="' << CORE_NS << '" xmlns:dc="' << CORE_NS_DC << '" ')
-      str << (+'xmlns:dcmitype="' << CORE_NS_DCMIT << '" xmlns:dcterms="' << CORE_NS_DCT << '" ')
-      str << (+'xmlns:xsi="' << CORE_NS_XSI << '">')
-      str << (+'<dc:creator>' << self.creator << '</dc:creator>')
-      str << (+'<dcterms:created xsi:type="dcterms:W3CDTF">' << (created || Time.now).strftime('%Y-%m-%dT%H:%M:%S') << 'Z</dcterms:created>')
+      str << '<cp:coreProperties xmlns:cp="' << CORE_NS << '" xmlns:dc="' << CORE_NS_DC << '" '
+      str << 'xmlns:dcmitype="' << CORE_NS_DCMIT << '" xmlns:dcterms="' << CORE_NS_DCT << '" '
+      str << 'xmlns:xsi="' << CORE_NS_XSI << '">'
+      str << '<dc:creator>' << self.creator << '</dc:creator>'
+      str << '<dcterms:created xsi:type="dcterms:W3CDTF">' << (created || Time.now).strftime('%Y-%m-%dT%H:%M:%S') << 'Z</dcterms:created>'
       str << '<cp:revision>0</cp:revision>'
       str << '</cp:coreProperties>'
     end