From 1d8a6db31c25bae39ece02efa565bcec8d1b0a03 Mon Sep 17 00:00:00 2001
From: Stefan Klug <stefan.klug@ideasonboard.com>
Date: Thu, 3 Apr 2025 17:49:06 +0200
Subject: libcamera: matrix: Replace SFINAE with static_asserts
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SFINAE is difficult to read and not needed in these cases. Replace it
with static_asserts. The idea came from [1] where it is stated:

"The use of enable_if seems misguided to me. SFINAE is useful for the
situation where we consider multiple candidates for something (overloads
or class template specializations) and try to choose the correct one,
without causing compilation to fail."

[1]: https://stackoverflow.com/questions/62109526/c-friend-template-that-use-sfinae

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
---
 include/libcamera/internal/matrix.h | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

(limited to 'include')

diff --git a/include/libcamera/internal/matrix.h b/include/libcamera/internal/matrix.h
index a055e692..b9c3d41e 100644
--- a/include/libcamera/internal/matrix.h
+++ b/include/libcamera/internal/matrix.h
@@ -19,14 +19,11 @@ namespace libcamera {
 
 LOG_DECLARE_CATEGORY(Matrix)
 
-#ifndef __DOXYGEN__
-template<typename T, unsigned int Rows, unsigned int Cols,
-	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
-#else
 template<typename T, unsigned int Rows, unsigned int Cols>
-#endif /* __DOXYGEN__ */
 class Matrix
 {
+	static_assert(std::is_arithmetic_v<T>, "Matrix type must be arithmetic");
+
 public:
 	Matrix()
 	{
@@ -123,16 +120,10 @@ Matrix<U, Rows, Cols> operator*(const Matrix<U, Rows, Cols> &m, T d)
 	return d * m;
 }
 
-#ifndef __DOXYGEN__
-template<typename T,
-	 unsigned int R1, unsigned int C1,
-	 unsigned int R2, unsigned int C2,
-	 std::enable_if_t<C1 == R2> * = nullptr>
-#else
-template<typename T, unsigned int R1, unsigned int C1, unsigned int R2, unsigned in C2>
-#endif /* __DOXYGEN__ */
-Matrix<T, R1, C2> operator*(const Matrix<T, R1, C1> &m1, const Matrix<T, R2, C2> &m2)
+template<typename T, unsigned int R1, unsigned int C1, unsigned int R2, unsigned int C2>
+constexpr Matrix<T, R1, C2> operator*(const Matrix<T, R1, C1> &m1, const Matrix<T, R2, C2> &m2)
 {
+	static_assert(C1 == R2, "Matrix dimensions must match for multiplication");
 	Matrix<T, R1, C2> result;
 
 	for (unsigned int i = 0; i < R1; i++) {
-- 
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