tawasuyu/taffy

This module should contain any types or code that is different depending
on whether we're compiling for std, alloc or just core.

diff --git a/Cargo.toml b/Cargo.toml
index 271404b3e..f130df418 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,9 +16,17 @@ circle-ci = { repository = "vislyhq/stretch", branch = "master" }
 maintenance = { status = "experimental" }
 
 [dependencies]
-hashbrown = "0.6.3"
+arrayvec = "0.5.1"
+hash32 = "0.1.1"
+hash32-derive = "0.1.0"
+heapless = "0.5.1"
 lazy_static = "1.4"
 spin = "0.5.2"
+typenum = "1.11.2"
+
+[dependencies.hashbrown]
+version = "0.6.3"
+optional = true
 
 [dependencies.serde]
 version = "1.0.102"
@@ -27,6 +35,7 @@ optional = true
 
 [features]
 default = ["std"]
+alloc = ["hashbrown"]
 std = []
 serde_camel_case = ["serde"]
 serde_kebab_case = ["serde"]
diff --git a/src/lib.rs b/src/lib.rs
index 2e1284112..226ce569e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -22,6 +22,7 @@ mod algo;
 mod forest;
 mod id;
 
+mod sys;
 pub use crate::node::Stretch;
 
 use core::any::Any;
diff --git a/src/sys.rs b/src/sys.rs
new file mode 100644
index 000000000..40156fb1b
--- /dev/null
+++ b/src/sys.rs
@@ -0,0 +1,69 @@
+#[cfg(feature = "std")]
+mod std {
+    pub type Map<K, V> = ::std::collections::HashMap<K, V>;
+    pub type Vec<A> = ::std::vec::Vec<A>;
+    pub type ChildrenVec<A> = ::std::vec::Vec<A>;
+    pub type ParentsVec<A> = ::std::vec::Vec<A>;
+
+    pub fn new_map_with_capacity<K, V>(capacity: usize) -> Map<K, V>
+    where
+        K: Eq + ::std::hash::Hash,
+    {
+        Map::with_capacity(capacity)
+    }
+
+    pub fn new_vec_with_capacity<A>(capacity: usize) -> Vec<A> {
+        Vec::with_capacity(capacity)
+    }
+}
+
+#[cfg(feature = "alloc")]
+mod alloc {
+    pub type Map<K, V> = ::hashbrown::HashMap<K, V>;
+    pub type Vec<A> = ::alloc::vec::Vec<A>;
+    pub type ChildrenVec<A> = ::alloc::vec::Vec<A>;
+    pub type ParentsVec<A> = ::alloc::vec::Vec<A>;
+
+    pub fn new_map_with_capacity<K, V>(capacity: usize) -> Map<K, V> {
+        Map::with_capacity(capacity)
+    }
+
+    pub fn new_vec_with_capacity<A>(capacity: usize) -> Vec<A> {
+        Vec::with_capacity(capacity)
+    }
+}
+
+#[cfg(all(not(feature = "alloc"), not(feature = "std")))]
+mod core {
+    use typenum::marker_traits::Unsigned;
+
+    type MaxNodeCount = heapless::consts::U256;
+    type MaxChildCount = heapless::consts::U16;
+    type MaxParentsCount = heapless::consts::U1;
+
+    pub type Map<K, V> = ::heapless::FnvIndexMap<K, V, MaxNodeCount>;
+    pub type Vec<A> = ::arrayvec::ArrayVec<[A; MaxNodeCount::USIZE]>;
+    pub type ChildrenVec<A> = ::arrayvec::ArrayVec<[A; MaxChildCount::USIZE]>;
+    pub type ParentsVec<A> = ::arrayvec::ArrayVec<[A; MaxParentsCount::USIZE]>;
+
+    pub fn new_map_with_capacity<K, V>(_capacity: usize) -> Map<K, V>
+    where
+        K: Eq + ::hash32::Hash,
+    {
+        Map::new()
+    }
+
+    pub fn new_vec_with_capacity<T, A>(_capacity: usize) -> ::arrayvec::ArrayVec<A>
+    where
+        A: ::arrayvec::Array<Item = T>,
+    {
+        ::arrayvec::ArrayVec::new()
+    }
+}
+
+#[cfg(feature = "alloc")]
+pub use self::alloc::*;
+#[cfg(all(not(feature = "alloc"), not(feature = "std")))]
+pub use self::core::*;
+#[cfg(feature = "std")]
+pub use self::std::*;