Operator precedence determines how Ruby groups expressions, method calls, and attached code blocks when more than one grouping is possible. section 6.3.4 section 6.1.1
Curly braces and do/end bind differently
Both `array.map { |n| n * 10 }` and `array.map do |n| n * 10 end` produce `[10, 20, 30]` when used alone. With `puts`, however, `puts array.map { |n| n * 10 }` attaches the block to `map`, while `puts array.map do |n| n * 10 end` attaches it to `puts`. The latter is effectively `puts(array.map) do |n| n * 10 end`; `map` receives no block and returns an enumerator, while `puts` ignores its block. section 6.3.4
Use precedence rules to read and write Ruby expressions carefully:
- Treat curly-brace blocks as binding more tightly than do/end blocks when a surrounding method call could claim the block. section 6.3.4
- Remember that `!` has higher precedence than `==`: `!x == 1` compares the negation of `x` with `1`, rather than negating the comparison. section 6.1.1
- Prefer parentheses around negated comparisons, as in `!(x == 1)`, even when Ruby does not strictly require them. section 6.1.1
- When a method seems to ignore a block, inspect precedence before assuming the method is broken; methods need not yield to supplied blocks. section 6.3.4
