cpp

#ifndef MYCPP_GC_STR_H

#define MYCPP_GC_STR_H

#include "mycpp/common.h"  // DISALLOW_COPY_AND_ASSIGN

#include "mycpp/gc_obj.h"  // GC_OBJ

#include "mycpp/hash.h"    // HashFunc

template <typename T>

class List;

class BigStr {

 public:

  // Don't call this directly.  Call NewStr() instead, which calls this.

  BigStr() {

  }

  char* data() {

    return data_;

  }

  // Call this after writing into buffer created by OverAllocatedStr()

  void MaybeShrink(int str_len);

  BigStr* at(int i);

  // TODO: take (start, end) for equality without allocation (not pos)

  int find(BigStr* needle, int pos = 0);

  int rfind(BigStr* needle);

  BigStr* slice(int begin);

  BigStr* slice(int begin, int end);

  BigStr* strip();

  // Used for CommandSub in osh/cmd_exec.py

  BigStr* rstrip(BigStr* chars);

  BigStr* rstrip();

  BigStr* lstrip(BigStr* chars);

  BigStr* lstrip();

  BigStr* ljust(int width, BigStr* fillchar);

  BigStr* rjust(int width, BigStr* fillchar);

  // Can take (start, end) so Tokens can be compared without allocation

  bool startswith(BigStr* s);

  bool endswith(BigStr* s);

  BigStr* replace(BigStr* old, BigStr* new_str);

  BigStr* replace(BigStr* old, BigStr* new_str, int count);

  BigStr* join(List<BigStr*>* items);

  List<BigStr*>* split(BigStr* sep);

  List<BigStr*>* split(BigStr* sep, int max_split);

  List<BigStr*>* splitlines(bool keep);

  // TODO: Move unicode functions out of mycpp runtime?  Because we won't match

  // Python exactly

  bool isdigit();

  bool isalpha();

  bool isupper();

  BigStr* upper();

  BigStr* lower();

  // Other options for fast comparison / hashing / string interning:

  // - unique_id_: an index into intern table.  I don't think this works unless

  //   you want to deal with rehashing all strings when the set grows.

  //   - although note that the JVM has -XX:StringTableSize=FIXED, which means

  //   - it can degrade into linked list performance

  // - Hashed strings become GLOBAL_STR().  Never deallocated.

  // - Hashed strings become part of the "large object space", which might be

  //   managed by mark and sweep.  This requires linked list overhead.

  //   (doubly-linked?)

  // - Intern strings at GARBAGE COLLECTION TIME, with

  //   LayoutForwarded::new_location_?  Is this possible?  Does it introduce

  //   too much coupling between strings, hash tables, and GC?

  static constexpr ObjHeader obj_header() {

    return ObjHeader::BigStr();

  }

  unsigned hash(HashFunc h);

  int len_;

  unsigned hash_ : 31;

  unsigned is_hashed_ : 1;

  char data_[1];  // flexible array

 private:

  int _strip_left_pos();

  int _strip_right_pos();

  DISALLOW_COPY_AND_ASSIGN(BigStr)

};

constexpr int kStrHeaderSize = offsetof(BigStr, data_);

// Note: for SmallStr, we might copy into the VALUE

inline void BigStr::MaybeShrink(int str_len) {

  len_ = str_len;

  data_[len_] = '\0';  // NUL terminate

}

inline int len(const BigStr* s) {

  return s->len_;

}

BigStr* StrFormat(const char* fmt, ...);

BigStr* StrFormat(BigStr* fmt, ...);

// NOTE: This iterates over bytes.

class StrIter {

 public:

  explicit StrIter(BigStr* s) : s_(s), i_(0), len_(len(s)) {

    // Cheney only: s_ could be moved during iteration.

    // gHeap.PushRoot(reinterpret_cast<RawObject**>(&s_));

  }

  ~StrIter() {

    // gHeap.PopRoot();

  }

  void Next() {

    i_++;

  }

  bool Done() {

    return i_ >= len_;

  }

  BigStr* Value();  // similar to at()

 private:

  BigStr* s_;

  int i_;

  int len_;

  DISALLOW_COPY_AND_ASSIGN(StrIter)

};

extern BigStr* kEmptyString;

// GlobalStr notes:

// - sizeof("foo") == 4, for the NUL terminator.

// - gc_heap_test.cc has a static_assert that GlobalStr matches BigStr.  We

// don't put it here because it triggers -Winvalid-offsetof

template <int N>

class GlobalStr {

  // A template type with the same layout as BigStr with length N-1 (which needs

  // a buffer of size N).  For initializing global constant instances.

 public:

  int len_;

  unsigned hash_ : 31;

  unsigned is_hashed_ : 1;

  const char data_[N];

  DISALLOW_COPY_AND_ASSIGN(GlobalStr)

};

union Str {

 public:

  // Instead of this at the start of every function:

  //   Str* s = nullptr;

  // It will now be:

  //   Str s(nullptr);

  //

  //   StackRoot _root(&s);

  explicit Str(BigStr* big) : big_(big) {

  }

  char* data() {

    return big_->data();

  }

  Str at(int i) {

    return Str(big_->at(i));

  }

  Str upper() {

    return Str(big_->upper());

  }

  uint64_t raw_bytes_;

  BigStr* big_;

  // TODO: add SmallStr, see mycpp/small_str_test.cc

};

inline int len(const Str s) {

  return len(s.big_);

}

// This macro is a workaround for the fact that it's impossible to have a

// a constexpr initializer for char[N].  The "String Literals as Non-Type

// Template Parameters" feature of C++ 20 would have done it, but it's not

// there.

//

// https://old.reddit.com/r/cpp_questions/comments/j0khh6/how_to_constexpr_initialize_class_member_thats/

// https://stackoverflow.com/questions/10422487/how-can-i-initialize-char-arrays-in-a-constructor

//

// TODO: Can we hash values at compile time so they can be in the intern table?

#define GLOBAL_STR(name, val)                                                \

  GcGlobal<GlobalStr<sizeof(val)>> _##name = {                               \

      ObjHeader::Global(TypeTag::BigStr),                                    \

      {.len_ = sizeof(val) - 1, .hash_ = 0, .is_hashed_ = 0, .data_ = val}}; \

  BigStr* name = reinterpret_cast<BigStr*>(&_##name.obj);

// New style for SmallStr compatibility

#define GLOBAL_STR2(name, val)                                               \

  GcGlobal<GlobalStr<sizeof(val)>> _##name = {                               \

      ObjHeader::Global(TypeTag::BigStr),                                    \

      {.len_ = sizeof(val) - 1, .hash_ = 0, .is_hashed_ = 0, .data_ = val}}; \

  Str name(reinterpret_cast<BigStr*>(&_##name.obj));

#endif  // MYCPP_GC_STR_H