feat(ecs): add tuple method to pop the last element

1 files changed, 81 insertions, 0 deletions

diff --git a/ecs/src/tuple.rs b/ecs/src/tuple.rs
index 682c11d..1434592 100644
--- a/ecs/src/tuple.rs
+++ b/ecs/src/tuple.rs
@@ -11,6 +11,14 @@ pub trait With<OtherElem>
     type With;
 }
 
+/// Used to remove the last element of a tuple type.
+///
+/// For example: `(u32, String, PathBuf)` becomes `(u32, String)`.
+pub trait WithoutLast
+{
+    type Return;
+}
+
 /// Used to make all elements of a tuple type wrapped in [`Option`].
 pub trait IntoInOptions
 {
@@ -65,6 +73,61 @@ macro_rules! tuple_reduce_elem_tuple {
     };
 }
 
+macro_rules! elem_type_by_index {
+    (overflow) => {
+        ()
+    };
+
+    ($index: tt) => {
+        paste! {
+            [<Elem $index>]
+        }
+    };
+}
+
+macro_rules! elem_by_index {
+    (overflow) => {
+        ()
+    };
+
+    ($index: tt, $self: ident) => {
+        $self.$index
+    };
+}
+
+pub trait Pop: WithoutLast
+{
+    type LastElem;
+
+    fn pop(self) -> (<Self as WithoutLast>::Return, Self::LastElem);
+}
+
+macro_rules! all_except_last {
+    (start $($rest: tt)*) => {
+        all_except_last!(@[] $($rest)*)
+    };
+
+    (@[$($included_elem: ident,)*] $elem: ident $($rest: tt)+) => {
+        all_except_last!(@[$($included_elem,)* $elem,] $($rest)*)
+    };
+
+    (@[$($included_elem: expr,)*] ($elem: expr) $($rest: tt)+) => {
+        all_except_last!(@[$($included_elem,)* $elem,] $($rest)*)
+    };
+
+    (@[$($included_elem: ident,)*] $elem: ident) => {
+        ($($included_elem,)*)
+    };
+
+    (@[$($included_elem: expr,)*] $elem: expr) => {
+        ($($included_elem,)*)
+    };
+
+    (@[]) => {
+        ()
+    };
+}
+
 macro_rules! impl_tuple_traits {
     ($cnt: tt) => {
         seq!(I in 0..$cnt {
@@ -73,6 +136,11 @@ macro_rules! impl_tuple_traits {
                 type With = (#(Elem~I,)* OtherElem,);
             }
 
+            impl<#(Elem~I,)*> WithoutLast for (#(Elem~I,)*)
+            {
+                type Return = all_except_last!(start #(Elem~I)*);
+            }
+
             impl<#(Element~I: 'static,)*> IntoInOptions for (#(Element~I,)*)
             {
                 type InOptions = (#(Option<Element~I>,)*);
@@ -122,6 +190,19 @@ macro_rules! impl_tuple_traits {
                     type Out = sub!($cnt - 1, tuple_reduce_elem_tuple);
                 }
             }
+
+            impl<#(Elem~I,)*> Pop for (#(Elem~I,)*)
+            {
+                type LastElem = sub!($cnt - 1, elem_type_by_index);
+
+                fn pop(self) -> (<Self as WithoutLast>::Return, Self::LastElem)
+                {
+                    (
+                        all_except_last!(start #((self.I))*),
+                        sub!($cnt - 1, elem_by_index, (self))
+                    )
+                }
+            }
         });
     };
 }