ruby - How does this code with send :[] work? -

the following code generates output of 9. understand send calling method :[], confused how parameters work.

 x = [1,2,3]  x.send :[]=,0,4                             #why x [4,2,3]  x[0] + x.[](1) + x.send(:[],2)              # 4 + 2 + 3 

how line 2 , line 3 work?

line 2 is

x.send :[]=,0,4 

that fancy way of writing this:

x[0] = 4 

(calling send allows call private methods though, , 1 difference between 2 syntaxes. also, object conceivably override send method, break first syntax.)

so line 2 has effect of writing 4 first spot in array.

now on line 3, see adding 3 things. here list of things adding:

• x[0] - first element
• x.[](1) - syntax accessing elements, accesses second element. syntax traditional method call, name of method happens [].
• x.send(:[], 2) - shows feature of ruby, send method. accesses third element.

so result 9, because third line adds first, second, , third elements of array.

these examples appear illustrate interesting point design of ruby language. specifically, array accesses implemented method calls. preferred syntax writing array x[0] = 4 , preferred syntax reading x[0], because syntax familiar programmers many different languages. however, reading , writing arrays implemented using method calls under hood, , that's why possible use other syntaxes more traditional method call.

a traditional method call looks this: object.foo(arg1, arg2, arg3, ...).

the send thing shown above useful feature of ruby allows specify method calling using symbol, instead of forcing type exact name. lets call private methods.