@@ -4,6 +4,7 @@ use crate::ids::Vector;
44use derive_generic_visitor:: * ;
55use std:: collections:: HashSet ;
66use std:: convert:: Infallible ;
7+ use std:: fmt:: Debug ;
78use std:: iter:: Iterator ;
89use std:: mem;
910use std:: ops:: Index ;
@@ -130,6 +131,27 @@ impl<T> RegionBinder<T> {
130131 skip_binder : x. move_under_binder ( ) ,
131132 }
132133 }
134+
135+ pub fn map_ref < U > ( & self , f : impl FnOnce ( & T ) -> U ) -> RegionBinder < U > {
136+ RegionBinder {
137+ regions : self . regions . clone ( ) ,
138+ skip_binder : f ( & self . skip_binder ) ,
139+ }
140+ }
141+
142+ /// Substitute the bound variables with erased lifetimes.
143+ pub fn erase ( self ) -> T
144+ where
145+ T : AstVisitable ,
146+ {
147+ let mut val = self . skip_binder ;
148+ let args = GenericArgs {
149+ regions : self . regions . map_ref_indexed ( |_, _| Region :: Erased ) ,
150+ ..GenericArgs :: empty ( GenericsSource :: Builtin )
151+ } ;
152+ val. drive_mut ( & mut SubstVisitor :: new ( & args) ) ;
153+ val
154+ }
133155}
134156
135157impl GenericArgs {
@@ -270,6 +292,90 @@ impl IntegerTy {
270292 }
271293}
272294
295+ /// A value of type `T` bound by the generic parameters of item
296+ /// `item`. Used when dealing with multiple items at a time, to
297+ /// ensure we don't mix up generics.
298+ ///
299+ /// To get the value, use `under_binder_of` or `subst_for`.
300+ #[ derive( Debug , Clone , Copy ) ]
301+ pub struct ItemBinder < ItemId , T > {
302+ pub item_id : ItemId ,
303+ val : T ,
304+ }
305+
306+ impl < ItemId , T > ItemBinder < ItemId , T >
307+ where
308+ ItemId : Debug + Copy + PartialEq ,
309+ {
310+ pub fn new ( item_id : ItemId , val : T ) -> Self {
311+ Self { item_id, val }
312+ }
313+
314+ pub fn as_ref ( & self ) -> ItemBinder < ItemId , & T > {
315+ ItemBinder {
316+ item_id : self . item_id ,
317+ val : & self . val ,
318+ }
319+ }
320+
321+ pub fn map_bound < U > ( self , f : impl FnOnce ( T ) -> U ) -> ItemBinder < ItemId , U > {
322+ ItemBinder {
323+ item_id : self . item_id ,
324+ val : f ( self . val ) ,
325+ }
326+ }
327+
328+ fn assert_item_id ( & self , item_id : ItemId ) {
329+ assert_eq ! (
330+ self . item_id, item_id,
331+ "Trying to use item bound for {:?} as if it belonged to {:?}" ,
332+ self . item_id, item_id
333+ ) ;
334+ }
335+
336+ /// Assert that the value is bound for item `item_id`, and returns it. This is used when we
337+ /// plan to store the returned value inside that item.
338+ pub fn under_binder_of ( self , item_id : ItemId ) -> T {
339+ self . assert_item_id ( item_id) ;
340+ self . val
341+ }
342+
343+ /// Given generic args for `item_id`, assert that the value is bound for `item_id` and
344+ /// substitute it with the provided generic arguments. Because the arguments are bound in the
345+ /// context of another item, so it the resulting substituted value.
346+ pub fn substitute < OtherItem : Debug + Copy + PartialEq > (
347+ self ,
348+ args : ItemBinder < OtherItem , & GenericArgs > ,
349+ ) -> ItemBinder < OtherItem , T >
350+ where
351+ ItemId : Into < AnyTransId > ,
352+ T : TyVisitable ,
353+ {
354+ args. map_bound ( |args| {
355+ assert_eq ! (
356+ args. target,
357+ GenericsSource :: item( self . item_id) ,
358+ "These `GenericArgs` are meant for {:?} but were used on {:?}" ,
359+ args. target,
360+ self . item_id
361+ ) ;
362+ let mut val = self . val ;
363+ val. substitute ( args) ;
364+ val
365+ } )
366+ }
367+ }
368+
369+ /// Dummy item identifier that represents the current item when not ambiguous.
370+ #[ derive( Debug , Clone , Copy , PartialEq , Eq ) ]
371+ pub struct CurrentItem ;
372+
373+ impl < T > ItemBinder < CurrentItem , T > {
374+ pub fn under_current_binder ( self ) -> T {
375+ self . val
376+ }
377+ }
378+
273379impl Ty {
274380 /// Return true if it is actually unit (i.e.: 0-tuple)
275381pub fn is_unit ( & self ) -> bool {
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