BLI: improve constructors and conversions to span

This allows us to avoid many calls to `as_span()` methods. I will
remove those in the next commit. Furthermore, constructors
of Vector and Array can convert from one type to another now.

I tested these changes on Linux with gcc and on Windows.

1 files changed, 17 insertions, 3 deletions

diff --git a/source/blender/blenlib/BLI_array.hh b/source/blender/blenlib/BLI_array.hh
index 18f9aad1000..c7a9c49c972 100644
--- a/source/blender/blenlib/BLI_array.hh
+++ b/source/blender/blenlib/BLI_array.hh
@@ -89,17 +89,19 @@ class Array {
   /**
    * Create a new array that contains copies of all values.
    */
-  Array(Span<T> values, Allocator allocator = {}) : allocator_(allocator)
+  template<typename U, typename std::enable_if_t<std::is_convertible_v<U, T>> * = nullptr>
+  Array(Span<U> values, Allocator allocator = {}) : allocator_(allocator)
   {
     size_ = values.size();
     data_ = this->get_buffer_for_size(values.size());
-    uninitialized_copy_n(values.data(), size_, data_);
+    uninitialized_convert_n<U, T>(values.data(), size_, data_);
   }
 
   /**
    * Create a new array that contains copies of all values.
    */
-  Array(const std::initializer_list<T> &values) : Array(Span<T>(values))
+  template<typename U, typename std::enable_if_t<std::is_convertible_v<U, T>> * = nullptr>
+  Array(const std::initializer_list<U> &values) : Array(Span<U>(values))
   {
   }
 
@@ -219,6 +221,18 @@ class Array {
     return MutableSpan<T>(data_, size_);
   }
 
+  template<typename U, typename std::enable_if_t<is_convertible_pointer_v<T, U>> * = nullptr>
+  operator Span<U>() const
+  {
+    return Span<U>(data_, size_);
+  }
+
+  template<typename U, typename std::enable_if_t<is_convertible_pointer_v<T, U>> * = nullptr>
+  operator MutableSpan<U>()
+  {
+    return MutableSpan<U>(data_, size_);
+  }
+
   Span<T> as_span() const
   {
     return *this;