Add format utility

src/arena_allocator.hpp

@@ -434,6 +434,40 @@ public:
     return current_block_ ? current_block_->size - current_block_->offset : 0;
   }
 
+  /**
+   * @brief Get all available space in the current block and claim it
+   * immediately.
+   *
+   * This method returns a pointer to all remaining space in the current block
+   * and immediately marks it as used in the arena. The caller should use
+   * realloc() to shrink the allocation to the actual amount needed.
+   *
+   * If no block exists or current block is full, creates a new block.
+   *
+   * @return Pointer to allocated space and the number of bytes allocated
+   * @note The caller must call realloc() to return unused space
+   * @note This is designed for speculative operations like printf formatting
+   * @note Postcondition: always returns at least 1 byte
+   */
+  struct AllocatedSpace {
+    char *ptr;
+    size_t allocated_bytes;
+  };
+
+  AllocatedSpace allocate_remaining_space() {
+    if (!current_block_ || available_in_current_block() == 0) {
+      add_block(initial_block_size_);
+    }
+
+    char *allocated_ptr = current_block_->data() + current_block_->offset;
+    size_t available = available_in_current_block();
+
+    // Claim all remaining space
+    current_block_->offset = current_block_->size;
+
+    return {allocated_ptr, available};
+  }
+
   /**
    * @brief Get the total number of blocks in the allocator.
    *