do..end vs curly braces for blocks in Ruby

The general convention is to use do..end for multi-line blocks and curly braces for single line blocks, but there is also a difference between the two that can be illustrated with this example:

puts [1,2,3].map{ |k| k+1 }234=> nilputs [1,2,3].map do |k| k+1; end#<Enumerator:0x0000010a06d140>=> nil

This means that {} has a higher precedence than do..end, so keep that in mind when deciding what you want to use.

P.S: One more example to keep in mind while you develop your preferences.

The following code:

task :rake => pre_rake_task do  somethingend

really means:

task(:rake => pre_rake_task){ something }

And this code:

task :rake => pre_rake_task {  something}

really means:

task :rake => (pre_rake_task { something })

So to get the actual definition that you want, with curly braces, you must do:

task(:rake => pre_rake_task) {  something}

Maybe using braces for parameters is something you want to do anyways, but if you don't it's probably best to use do..end in these cases to avoid this confusion.

From Programming Ruby:

Braces have a high precedence; do has a low precedence. If the method invocation has parameters that are not enclosed in parentheses, the brace form of a block will bind to the last parameter, not to the overall invocation. The do form will bind to the invocation.

So the code

f param {do_something()}

Binds the block to the param variable while the code

f param do do_something() end

Binds the block to the function f.

However this is a non-issue if you enclose function arguments in parenthesis.

There a few points of view on this, it's really a matter of personal preference. Many rubyists take the approach you do. However, two other styles that are common is to always use one or the other, or to use {} for blocks that return values, and do ... end for blocks that are executed for side effects.