The problem with this is that it will not actually parse double in IEEE 754, as you will accumulate inaccuracies at every step of the loop. In theory, when parsing a float, you are supposed to return the floating point that is closest to the original string number. Your code will not do that. Even if you accept the inaccuracy, if you for some reason load the JSON using a runtime library, you'll get different numbers and consequently and result that depend on those numbers. For my use-case this was not acceptable unfortunately..