[echaozh]

Though people often criticise immutability on the ground that the machine code mutates registers and memory addresses as they're scarce resource, the compilers don't often generate such code directly. The compilers generate IR in the static single assignment form for better analysis and optimisation. That said, you should know why mutation is not inherently good, but a compromise to the pathetic reality. And now you know the technique to avoid mutation in general as well.