日期：
来源：架构文摘收集编辑：
作者 | Casey Muratori、译者 | 弯月
责编 | 苏宓、出品 | CSDN（ID：CSDNnews）
使用多态代替“if/else”和“switch”；
代码不应该知道使用对象的内部结构；
严格控制函数的规模；
函数应该只做一件事；
“DRY”（Don’t Repeat Yourself）：不要重复自己。
/* ========================================================================
LISTING 22
======================================================================== */
class shape_base
{
public:
shape_base() {}
virtual f32 Area() = 0;
};
class square : public shape_base
{
public:
square(f32 SideInit) : Side(SideInit) {}
virtual f32 Area() {return Side*Side;}
private:
f32 Side;
};
class rectangle : public shape_base
{
public:
rectangle(f32 WidthInit, f32 HeightInit) : Width(WidthInit), Height(HeightInit) {}
virtual f32 Area() {return Width*Height;}
private:
f32 Width, Height;
};
class triangle : public shape_base
{
public:
triangle(f32 BaseInit, f32 HeightInit) : Base(BaseInit), Height(HeightInit) {}
virtual f32 Area() {return 0.5f*Base*Height;}
private:
f32 Base, Height;
};
class circle : public shape_base
{
public:
circle(f32 RadiusInit) : Radius(RadiusInit) {}
virtual f32 Area() {return Pi32*Radius*Radius;}
private:
f32 Radius;
};
/* ========================================================================
LISTING 23
======================================================================== */
f32 TotalAreaVTBL(u32 ShapeCount, shape_base **Shapes)
{
f32 Accum = 0.0f;
for(u32 ShapeIndex = 0; ShapeIndex < ShapeCount; ++ShapeIndex)
{
Accum += Shapes[ShapeIndex]->Area();
}
return Accum;
}
/* ========================================================================
LISTING 24
======================================================================== */
f32 TotalAreaVTBL4(u32 ShapeCount, shape_base **Shapes)
{
f32 Accum0 = 0.0f;
f32 Accum1 = 0.0f;
f32 Accum2 = 0.0f;
f32 Accum3 = 0.0f;
u32 Count = ShapeCount/4;
while(Count--)
{
Accum0 += Shapes[0]->Area();
Accum1 += Shapes[1]->Area();
Accum2 += Shapes[2]->Area();
Accum3 += Shapes[3]->Area();
Shapes += 4;
}
f32 Result = (Accum0 + Accum1 + Accum2 + Accum3);
return Result;
}
/* ========================================================================
LISTING 25
======================================================================== */
enum shape_type : u32
{
Shape_Square,
Shape_Rectangle,
Shape_Triangle,
Shape_Circle,
Shape_Count,
};
struct shape_union
{
shape_type Type;
f32 Width;
f32 Height;
};
f32 GetAreaSwitch(shape_union Shape)
{
f32 Result = 0.0f;
switch(Shape.Type)
{
case Shape_Square: {Result = Shape.Width*Shape.Width;} break;
case Shape_Rectangle: {Result = Shape.Width*Shape.Height;} break;
case Shape_Triangle: {Result = 0.5f*Shape.Width*Shape.Height;} break;
case Shape_Circle: {Result = Pi32*Shape.Width*Shape.Width;} break;
case Shape_Count: {} break;
}
return Result;
}
/* ========================================================================
LISTING 26
======================================================================== */
f32 TotalAreaSwitch(u32 ShapeCount, shape_union *Shapes)
{
f32 Accum = 0.0f;
for(u32 ShapeIndex = 0; ShapeIndex < ShapeCount; ++ShapeIndex)
{
Accum += GetAreaSwitch(Shapes[ShapeIndex]);
}
return Accum;
}
f32 TotalAreaSwitch4(u32 ShapeCount, shape_union *Shapes)
{
f32 Accum0 = 0.0f;
f32 Accum1 = 0.0f;
f32 Accum2 = 0.0f;
f32 Accum3 = 0.0f;
ShapeCount /= 4;
while(ShapeCount--)
{
Accum0 += GetAreaSwitch(Shapes[0]);
Accum1 += GetAreaSwitch(Shapes[1]);
Accum2 += GetAreaSwitch(Shapes[2]);
Accum3 += GetAreaSwitch(Shapes[3]);
Shapes += 4;
}
f32 Result = (Accum0 + Accum1 + Accum2 + Accum3);
return Result;
}
case Shape_Square: {Result = Shape.Width*Shape.Width;} break;
case Shape_Rectangle: {Result = Shape.Width*Shape.Height;} break;
case Shape_Triangle: {Result = 0.5f*Shape.Width*Shape.Height;} break;
case Shape_Circle: {Result = Pi32*Shape.Width*Shape.Width;} break;
/* ========================================================================
LISTING 27
======================================================================== */
f32 const CTable[Shape_Count] = {1.0f, 1.0f, 0.5f, Pi32};
f32 GetAreaUnion(shape_union Shape)
{
f32 Result = CTable[Shape.Type]*Shape.Width*Shape.Height;
return Result;
}
/* ========================================================================
LISTING 32
======================================================================== */
class shape_base
{
public:
shape_base() {}
virtual f32 Area() = 0;
virtual u32 CornerCount() = 0;
};
class square : public shape_base
{
public:
square(f32 SideInit) : Side(SideInit) {}
virtual f32 Area() {return Side*Side;}
virtual u32 CornerCount() {return 4;}
private:
f32 Side;
};
class rectangle : public shape_base
{
public:
rectangle(f32 WidthInit, f32 HeightInit) : Width(WidthInit), Height(HeightInit) {}
virtual f32 Area() {return Width*Height;}
virtual u32 CornerCount() {return 4;}
private:
f32 Width, Height;
};
class triangle : public shape_base
{
public:
triangle(f32 BaseInit, f32 HeightInit) : Base(BaseInit), Height(HeightInit) {}
virtual f32 Area() {return 0.5f*Base*Height;}
virtual u32 CornerCount() {return 3;}
private:
f32 Base, Height;
};
class circle : public shape_base
{
public:
circle(f32 RadiusInit) : Radius(RadiusInit) {}
virtual f32 Area() {return Pi32*Radius*Radius;}
virtual u32 CornerCount() {return 0;}
private:
f32 Radius;
};
f32 CornerAreaVTBL(u32 ShapeCount, shape_base **Shapes)
{
f32 Accum = 0.0f;
for(u32 ShapeIndex = 0; ShapeIndex < ShapeCount; ++ShapeIndex)
{
Accum += (1.0f / (1.0f + (f32)Shapes[ShapeIndex]->CornerCount())) * Shapes[ShapeIndex]->Area();
}
return Accum;
}
f32 CornerAreaVTBL4(u32 ShapeCount, shape_base **Shapes)
{
f32 Accum0 = 0.0f;
f32 Accum1 = 0.0f;
f32 Accum2 = 0.0f;
f32 Accum3 = 0.0f;
u32 Count = ShapeCount/4;
while(Count--)
{
Accum0 += (1.0f / (1.0f + (f32)Shapes[0]->CornerCount())) * Shapes[0]->Area();
Accum1 += (1.0f / (1.0f + (f32)Shapes[1]->CornerCount())) * Shapes[1]->Area();
Accum2 += (1.0f / (1.0f + (f32)Shapes[2]->CornerCount())) * Shapes[2]->Area();
Accum3 += (1.0f / (1.0f + (f32)Shapes[3]->CornerCount())) * Shapes[3]->Area();
Shapes += 4;
}
f32 Result = (Accum0 + Accum1 + Accum2 + Accum3);
return Result;
}
/* ========================================================================
LISTING 34
======================================================================== */
u32 GetCornerCountSwitch(shape_type Type)
{
u32 Result = 0;
switch(Type)
{
case Shape_Square: {Result = 4;} break;
case Shape_Rectangle: {Result = 4;} break;
case Shape_Triangle: {Result = 3;} break;
case Shape_Circle: {Result = 0;} break;
case Shape_Count: {} break;
}
return Result;
}
/* ========================================================================
LISTING 35
======================================================================== */
f32 CornerAreaSwitch(u32 ShapeCount, shape_union *Shapes)
{
f32 Accum = 0.0f;
for(u32 ShapeIndex = 0; ShapeIndex < ShapeCount; ++ShapeIndex)
{
Accum += (1.0f / (1.0f + (f32)GetCornerCountSwitch(Shapes[ShapeIndex].Type))) * GetAreaSwitch(Shapes[ShapeIndex]);
}
return Accum;
}
f32 CornerAreaSwitch4(u32 ShapeCount, shape_union *Shapes)
{
f32 Accum0 = 0.0f;
f32 Accum1 = 0.0f;
f32 Accum2 = 0.0f;
f32 Accum3 = 0.0f;
ShapeCount /= 4;
while(ShapeCount--)
{
Accum0 += (1.0f / (1.0f + (f32)GetCornerCountSwitch(Shapes[0].Type))) * GetAreaSwitch(Shapes[0]);
Accum1 += (1.0f / (1.0f + (f32)GetCornerCountSwitch(Shapes[1].Type))) * GetAreaSwitch(Shapes[1]);
Accum2 += (1.0f / (1.0f + (f32)GetCornerCountSwitch(Shapes[2].Type))) * GetAreaSwitch(Shapes[2]);
Accum3 += (1.0f / (1.0f + (f32)GetCornerCountSwitch(Shapes[3].Type))) * GetAreaSwitch(Shapes[3]);
Shapes += 4;
}
f32 Result = (Accum0 + Accum1 + Accum2 + Accum3);
return Result;
}
/* ========================================================================
LISTING 36
======================================================================== */
f32 const CTable[Shape_Count] = {1.0f / (1.0f + 4.0f), 1.0f / (1.0f + 4.0f), 0.5f / (1.0f + 3.0f), Pi32};
f32 GetCornerAreaUnion(shape_union Shape)
{
f32 Result = CTable[Shape.Type]*Shape.Width*Shape.Height;
return Result;
}
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