Implement SMatrix::from_array_storage and use it in matriX! impl

This allows us to avoid injecting unsafe code into every macro
invocation, which seems desirable.

nalgebra-macros/src/lib.rs

@@ -90,12 +90,9 @@ pub fn matrix(stream: TokenStream) -> TokenStream {
     let array_tokens = matrix.col_major_array_tokens();
 
     //  TODO: Use quote_spanned instead??
-    // TODO: Avoid use of unsafe here
     let output = quote! {
-        unsafe {
         nalgebra::SMatrix::<_, #row_dim, #col_dim>
-            ::from_data_statically_unchecked(nalgebra::ArrayStorage(#array_tokens))
-        }
+            ::from_array_storage(nalgebra::ArrayStorage(#array_tokens))
     };
 
     proc_macro::TokenStream::from(output)

src/base/array_storage.rs

@@ -25,6 +25,7 @@ use crate::base::storage::{
     ContiguousStorage, ContiguousStorageMut, Owned, ReshapableStorage, Storage, StorageMut,
 };
 use crate::base::Scalar;
+use crate::SMatrix;
 
 /*
  *
@@ -299,3 +300,14 @@ where
         self.as_slice().iter().fold(0, |acc, e| acc + e.extent())
     }
 }
+
+// TODO: Where to put this impl block?
+impl<T, const R: usize, const C: usize> SMatrix<T, R, C> {
+    /// Creates a new statically-allocated matrix from the given [ArrayStorage].
+    #[inline(always)]
+    pub const fn from_array_storage(storage: ArrayStorage<T, R, C>) -> Self {
+        // This is sound because the row and column types are exactly the same as that of the
+        // storage, so there can be no mismatch
+        unsafe { Self::from_data_statically_unchecked(storage) }
+    }
+}