rust - Is it possible to access the type of a struct member for function signatures or declarations? -

when defining implementations in macros, might useful access struct members type avoid having pass argument. (see this question)

impl partialeq<u32> mystruct { ... } 

is there way access type of struct member without knowing in advance type is?

impl partialeq<typeof(mystruct.member)> mystruct { ... } 

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in case it's helpful, abbreviated example of why i'm interested this:

struct_bitflag_impl!(     pub struct myflag(u8);,     myflag, u8);  //          ^^ how avoid having arg? //             (used ``impl partialeq<$t_internal> $p``) //             couldn't discovered `myflag.0` ?  // macro  macro_rules! struct_bitflag_impl {     ($struct_p_def: item, $p:ident, $t_internal:ty) => {          #[derive(partialeq, eq, copy, clone, debug)]         $struct_p_def          impl ::std::ops::bitand $p {             type output = $p;             fn bitand(self, _rhs: $p) -> $p { $p(self.0 & _rhs.0) }         }         impl ::std::ops::bitor $p {             type output = $p;             fn bitor(self, _rhs: $p) -> $p { $p(self.0 | _rhs.0) }         }         impl ::std::ops::bitxor $p {             type output = $p;             fn bitxor(self, _rhs: $p) -> $p { $p(self.0 ^ _rhs.0) }         }          impl ::std::ops::not $p {             type output = $p;             fn not(self) -> $p { $p(!self.0) }         }          // support comparison base-type.         impl partialeq<$t_internal> $p {             fn eq(&self, other: &t_internal) -> bool {                 self.0 == *other             }         }         // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^         //       how avoid using 't_internal' here?     } } 

no, general typeof(type::field) can used in type position not exist.

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regarding example in question, looks expecting special kind of item: tuple-struct 1 field. so, instead of accepting $item fragment, can simulate syntax yourself:

macro_rules! foo {     (pub struct $name:ident ( $ty:ident ) ) => {         pub struct $name($ty);          impl $name {             pub fn bar() {                  println!("{}", stringify!($ty));              }         }     } }  foo!(     pub struct peter(u8) );  fn main() {     peter::bar(); } 

that way have specify once. however, works 1 kind of tuple-struct definition, not kinds of items. use case suggests more or less interested in special case.

if want allow different kinds of struct definitions, need add more macro-rules macro allow different syntax. see example, here code allow pub , non-pub tuple-struct definitions. expanded more.