That makes sense, thank you! It does make it a little confusing that a special case was made for pointers to arrays that violates that rule, but it's a pretty rare use case anyway.
Thanks for pointing this out, it was driving me crazy. On Thursday, July 20, 2017 at 2:47:12 AM UTC-4, Lyuben Blagoev wrote: > > I think the behavior is defined with the following statement in the spec: > > Primary expressions are the operands for unary and binary expressions. > > x[0] is a primary expression, so it is the operand for the unary > expression, thus the expression is avaluated as *(x[0]). > > On Thu, Jul 20, 2017 at 4:07 AM, Ian Lance Taylor <ia...@golang.org > <javascript:>> wrote: > >> On Wed, Jul 19, 2017 at 4:10 PM, <adrian...@gmail.com <javascript:>> >> wrote: >> > >> > The EBNF specifies the syntax, not the behavior. EBNF does not indicate >> the >> > order of evaluation of source code, only the order of characters in the >> > source code. >> >> Fair point. In this case it is also intended to indicate the >> precedence. In fact, in every case I know of, it indicates the >> precedence. >> >> Ian >> >> > On Wednesday, July 19, 2017 at 6:59:29 PM UTC-4, Ian Lance Taylor wrote: >> >> >> >> On Wed, Jul 19, 2017 at 3:28 PM, <adrian...@gmail.com> wrote: >> >> > >> >> > A question on Stack Overflow led me to carefully examine the spec >> and I >> >> > feel like there may be some detail that's missing - the behavior is >> easy >> >> > enough to work with, but it's effectively undefined according to the >> >> > language spec. Specifically, with a variable x of type *[]string for >> >> > example, *x[0] will not work because it is evaluated as *(x[0]), not >> as >> >> > (*x)[0]. This is unexpected based on the spec because the only >> >> > specifications that could apply are the general order of evaluation, >> which >> >> > is left to right (not the case here), and operator precedence which >> states >> >> > that pointer dereference is a unary operator and unary operators have >> >> > highest precedence (again clearly not what's happening). >> >> > >> >> > The closest it comes to explaining this behavior is in the section on >> >> > address operators, which implies that the address operator & applies >> to the >> >> > entire slice expression next to it (or struct field selector, etc). >> This >> >> > leaves one to assume the same implication applies to the pointer >> dereference >> >> > operator as well. >> >> > >> >> > Is there something covering this that I glossed over reading the >> spec? >> >> > If it's not just something I missed, is this worth clarifying in the >> spec, >> >> > without changing the behavior (purely a documentation change)? >> >> >> >> This is expressed in the EBNF grammar in the language spec. x[0] is a >> >> PrimaryExpr. *x[0] is a unary_op applied to a PrimaryExpr. >> >> >> >> Ian >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups >> > "golang-nuts" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an >> > email to golang-nuts...@googlegroups.com <javascript:>. >> > For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
