FormatStringImpl.h

#pragma once
 
#include <array>
#include <tuple>
#include <utility>
 
template <typename... ARGS>
class plFormatStringImpl : public plFormatString
{
  // this is the size of the temp buffer that BuildString functions get for writing their result to.
  // The buffer is always available and allocated on the stack, so this prevents the need for memory allocations.
  // If a BuildString function requires no storage at all, it can return an plStringView to unrelated memory
  // (e.g. if the memory already exists).
  // If a BuildString function requires more storage, it may need to do some trickery.
  // For an example look at BuildString for plArgErrorCode, which uses an increased thread_local temp buffer.
  static constexpr plUInt32 TempStringLength = 64;
  // Maximum number of parameters. Results in compilation error if exceeded.
  static constexpr plUInt32 MaxNumParameters = 12;
 
public:
  plFormatStringImpl(plStringView sFormat, ARGS&&... args)
    : m_Arguments(std::forward<ARGS>(args)...)
  {
    m_sString = sFormat;
  }
 
  plFormatStringImpl(const char* szFormat, ARGS&&... args)
    : m_Arguments(std::forward<ARGS>(args)...)
  {
    m_sString = szFormat;
  }
 
  virtual plStringView GetText(plStringBuilder& ref_sStorage) const override
  {
    if (m_sString.IsEmpty())
    {
      return {};
    }
 
    plStringView param[MaxNumParameters];
 
    char tmp[MaxNumParameters][TempStringLength];
    ReplaceString<0>(tmp, param);
 
    return BuildFormattedText(ref_sStorage, param, MaxNumParameters);
  }
 
  virtual const char* GetTextCStr(plStringBuilder& out_sString) const override
  {
    plStringView param[MaxNumParameters];
 
    char tmp[MaxNumParameters][TempStringLength];
    ReplaceString<0>(tmp, param);
 
    return BuildFormattedText(out_sString, param, MaxNumParameters).GetStartPointer();
  }
 
private:
  template <plInt32 N>
  typename std::enable_if<sizeof...(ARGS) != N>::type ReplaceString(char tmp[MaxNumParameters][TempStringLength], plStringView* pViews) const
  {
    static_assert(N < MaxNumParameters, "Maximum number of format arguments reached");
 
    // using a free function allows to overload with various different argument types
    pViews[N] = BuildString(tmp[N], TempStringLength - 1, std::get<N>(m_Arguments));
 
    // Recurse, chip off one argument
    ReplaceString<N + 1>(tmp, pViews);
  }
 
  // Recursion end if we reached the number of arguments.
  template <plInt32 N>
  typename std::enable_if<sizeof...(ARGS) == N>::type ReplaceString(char tmp[MaxNumParameters][TempStringLength], plStringView* pViews) const
  {
  }
 
 
  // stores the arguments
  std::tuple<ARGS...> m_Arguments;
};