On Wed, 13 Jan 2010, Larry Evans wrote:
On 01/13/10 11:17, dherring@ll.mit.edu wrote:
On Tue, 12 Jan 2010, Larry Evans wrote:
On 01/12/10 11:29, dherring@ll.mit.edu wrote:
I wrote a similar utility, but made different tradeoffs. The basic usage looks like
Indentation nl; // takes optional max depth and depth/level params Indentation::Indent in(nl); // could have used a reference notation Indentation::Outdent out(nl); std::ostream os; os << nl "class x << nl << '{' << in /* or nl.in */ << nl << "int x;" << nl << "int y;" << out << nl << "};"
And assuming an initial depth of 0, this outputs " class x { int x; int y; };"
- distinguishes between indenting and normal newlines
I'm not sure what this means. Does it mean that to indent a line, you have to use nl, as shown in this snippet of the code you posted:
<< nl << "int x;"
If so, then I'm not sure that's an advantage. Could you please elaborate on what you mean?
Yes. In my work, this is a great advantage. People don't like text with trailing whitespaces, but they want blank lines for visual separation.
Doesn't:
os<<nl<<"\n"
produce trailing whitespace whose length is the current indentation level which is stored somewhere in nl. Hmm... What's the return type from os<<nl. I'm guessing it must be typeof(nl)& because otherwise, how would the change in indentation be communicated from the <<out at the end of the output line:
<< nl << "int y;" << out
Could you clarify how out changes the indentation? Does it modify the nl that occurs at the beginning?
In my implementation, [pseudocode] operator<<(\n) is an ordinary newline operator<<(nl) inserts a newline followed by the current indentation operator<<(nl.in) increments the depth of nl but produces no output operator<<(nl.out) decrements the depth of nl but produces no output Since all indentation operations occur in operator<<(), they all happen in the expected sequential order.
I could see an argument for having \n indent and nl not; it may make it easier to compose indentation with output functions that do not understand it. However, my experience has been that an indenting newlines semantically belong before the line text while a traditional \n appears after the text. This creates a mismatch; a general indentation tool should probably have a (scoped) mechanism for switching behaviors.
Example: (pseudo C++) ... However, I don't see where the indentation for the vector comes from because there's no calls to nl in the operator<< specializtion for vector<int>. Am I missing something?
I was suggesting that an implementation could hook into \n for its indentation. Mine doesn't because the semantics usually aren't right anyway. Indenting newlines work best in a prefix position; normal newlines usually appear postfix. However, a general indentation utility should probably allow \n to behave as nl. i.e. os << nl << "foo" << nl.in << nl; nl.wrap(os) << "bar\n"; // to reuse printers ignorant of indentation os << "baz\nquux"; would output " foo bar baz quux "
- possible to maintain several indentation systems
Could you describe when this would be an advantage?
This is rarely useful, but there are times when indentation differentiates between classes of output line. This is naturally represented by having one indentation object per class.
Couldn't this be handled by defining operator<< for each class?
Here "classes of output" was not meant in the C++ usage of "class" but rather "category". So you can't have a custom operator<<; indentation might be specified by a value in the object, by the identity of the object, by the identity of the containing object, ... Example you might see in a foreign language course: Tom Mary Hi! How are you? Good, and you? Fine, thank you. Which could be written as os << TomNL << "Tom" << MaryNL << "Mary" << TomNL << "Hi!" << MaryNL << "How are you?" ... Later, Daniel