BLI: make some spans default constructible

`GSpan` and spans based on virtual arrays were not default constructible
before, which made them hard to use sometimes. It's generally fine for
spans to be empty.

The main thing the keep in mind is that the type pointer in `GSpan` may
be null now. Generally, code receiving spans as input can assume that
the type is not-null, but sometimes that may be valid. The old #type() method
that returned a reference to the type still exists. It asserts when the
type is null.

1 files changed, 48 insertions, 16 deletions

diff --git a/source/blender/blenlib/BLI_generic_span.hh b/source/blender/blenlib/BLI_generic_span.hh
index 4c0bfc83ba8..0a40201634a 100644
--- a/source/blender/blenlib/BLI_generic_span.hh
+++ b/source/blender/blenlib/BLI_generic_span.hh
@@ -16,20 +16,30 @@ namespace blender {
  */
 class GSpan {
  protected:
-  const CPPType *type_;
-  const void *data_;
-  int64_t size_;
+  const CPPType *type_ = nullptr;
+  const void *data_ = nullptr;
+  int64_t size_ = 0;
 
  public:
-  GSpan(const CPPType &type, const void *buffer, int64_t size)
-      : type_(&type), data_(buffer), size_(size)
+  GSpan() = default;
+
+  GSpan(const CPPType *type, const void *buffer, int64_t size)
+      : type_(type), data_(buffer), size_(size)
   {
     BLI_assert(size >= 0);
     BLI_assert(buffer != nullptr || size == 0);
-    BLI_assert(type.pointer_has_valid_alignment(buffer));
+    BLI_assert(type->pointer_has_valid_alignment(buffer));
+  }
+
+  GSpan(const CPPType &type, const void *buffer, int64_t size) : GSpan(&type, buffer, size)
+  {
+  }
+
+  GSpan(const CPPType &type) : type_(&type)
+  {
   }
 
-  GSpan(const CPPType &type) : GSpan(type, nullptr, 0)
+  GSpan(const CPPType *type) : type_(type)
   {
   }
 
@@ -41,9 +51,15 @@ class GSpan {
 
   const CPPType &type() const
   {
+    BLI_assert(type_ != nullptr);
     return *type_;
   }
 
+  const CPPType *type_ptr() const
+  {
+    return type_;
+  }
+
   bool is_empty() const
   {
     return size_ == 0;
@@ -76,7 +92,7 @@ class GSpan {
     BLI_assert(start >= 0);
     BLI_assert(size >= 0);
     const int64_t new_size = std::max<int64_t>(0, std::min(size, size_ - start));
-    return GSpan(*type_, POINTER_OFFSET(data_, type_->size() * start), new_size);
+    return GSpan(type_, POINTER_OFFSET(data_, type_->size() * start), new_size);
   }
 
   GSpan slice(const IndexRange range) const
@@ -91,20 +107,30 @@ class GSpan {
  */
 class GMutableSpan {
  protected:
-  const CPPType *type_;
-  void *data_;
-  int64_t size_;
+  const CPPType *type_ = nullptr;
+  void *data_ = nullptr;
+  int64_t size_ = 0;
 
  public:
-  GMutableSpan(const CPPType &type, void *buffer, int64_t size)
-      : type_(&type), data_(buffer), size_(size)
+  GMutableSpan() = default;
+
+  GMutableSpan(const CPPType *type, void *buffer, int64_t size)
+      : type_(type), data_(buffer), size_(size)
   {
     BLI_assert(size >= 0);
     BLI_assert(buffer != nullptr || size == 0);
-    BLI_assert(type.pointer_has_valid_alignment(buffer));
+    BLI_assert(type->pointer_has_valid_alignment(buffer));
+  }
+
+  GMutableSpan(const CPPType &type, void *buffer, int64_t size) : GMutableSpan(&type, buffer, size)
+  {
+  }
+
+  GMutableSpan(const CPPType &type) : type_(&type)
+  {
   }
 
-  GMutableSpan(const CPPType &type) : GMutableSpan(type, nullptr, 0)
+  GMutableSpan(const CPPType *type) : type_(type)
   {
   }
 
@@ -116,14 +142,20 @@ class GMutableSpan {
 
   operator GSpan() const
   {
-    return GSpan(*type_, data_, size_);
+    return GSpan(type_, data_, size_);
   }
 
   const CPPType &type() const
   {
+    BLI_assert(type_ != nullptr);
     return *type_;
   }
 
+  const CPPType *type_ptr() const
+  {
+    return type_;
+  }
+
   bool is_empty() const
   {
     return size_ == 0;