try this

include/fls/io/mmap.hpp

@@ -7,10 +7,6 @@
 namespace fastlanes {
 class Mmap {
 public:
-	static std::byte* Resize(bsz_t bsz, int& fd);
-	template <typename T>
-	static T*   Resize(bsz_t bsz, int& fd);
-	static void Close(void* p, bsz_t bsz, int& fd);
 };
 } // namespace fastlanes
 

src/io/mmap.cpp

@@ -1,35 +1,6 @@
 #include "fls/io/mmap.hpp"
-#include <cstring>
-#include <sys/fcntl.h>
-#if defined(_WIN32)
-#include <windows.h> // For Windows memory-mapping
-#define open  _open
-#define close _close
-#else
-#include <sys/mman.h> // For POSIX memory-mapping
-#endif
-#include <sys/stat.h>
-#include <unistd.h>
 
-namespace fastlanes {
-
-void Mmap::Close(void* p, bsz_t bsz, int& fd) {
-	/**/
-	if (munmap(p, bsz) == -1) { throw std::runtime_error(strerror(errno)); }
-	close(fd);
-}
-
-std::byte* Mmap::Resize(bsz_t bsz, int& fd) {
-	if (ftruncate(fd, static_cast<off_t>(bsz)) == -1) { throw std::runtime_error("Error resizing the file"); }
-	auto* p = reinterpret_cast<std::byte*>(mmap(nullptr, bsz, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
-	return p;
-}
 
-template <typename T>
-T* Mmap::Resize(bsz_t bsz, int& fd) {
-	return reinterpret_cast<T*>(Resize(bsz, fd));
-}
-
-template uint64_t* Mmap::Resize<>(bsz_t bsz, int& fd);
+namespace fastlanes {
 
 } // namespace fastlanes