苹果的系统默认字体是苹方字体吗

现今UI设计师都是按照PingFangSC字体来设计效果，每次写都是长长的一段代码，如下：

UIFont *font = [UIFont fontWithName:@"PingFangSC-Regular" size:16.0];
UIFont *font = [UIFont fontWithName:@"PingFangSC-Medium" size:16];

尤其是中间的字符串，特别容易写错，Xcode还没有提示。
so，为了防止写错，就写了一个分类来解决这个问题。

typedef NS_ENUM(NSUInteger, CMJPingFangSCType) {
    CMJPingFangSCTypeThin,
    CMJPingFangSCTypeUltralight,
    CMJPingFangSCTypeLight,
    CMJPingFangSCTypeRegular,
    CMJPingFangSCTypeMedium,
    CMJPingFangSCTypeSemibold,
};

@interface UIFont (CMJFont)
+ (UIFont *)cmj_PingFangSCFontWithType:(CMJPingFangSCType)type fontSize:(CGFloat)size;
@end

@implementation UIFont (CMJFont)
+ (UIFont *)cmj_PingFangSCFontWithType:(CMJPingFangSCType)type fontSize:(CGFloat)size
{
    UIFont *font = nil;
    switch (type) {
        case CMJPingFangSCTypeThin:
            font = [UIFont fontWithName:@"PingFangSC-Thin" size:size];
            break;
            
        case CMJPingFangSCTypeUltralight:
            font = [UIFont fontWithName:@"PingFangSC-Ultralight" size:size];
            break;
            
        case CMJPingFangSCTypeLight:
            font = [UIFont fontWithName:@"PingFangSC-Light" size:size];
            break;
            
        case CMJPingFangSCTypeRegular:
            font = [UIFont fontWithName:@"PingFangSC-Regular" size:size];
            break;
            
        case CMJPingFangSCTypeMedium:
            font = [UIFont fontWithName:@"PingFangSC-Medium" size:size];
            break;
            
        case CMJPingFangSCTypeSemibold:
            font = [UIFont fontWithName:@"PingFangSC-Semibold" size:size];
            break;
            
        default:
            break;
    }
    return font;
}

@end

好久好久之后，直到有一天，和UI设计师聊天，说，
“苹果默认的字体不就是苹方字体吗？”
“What？”
咱也不知道，咱也不敢问，怎么办，回去打印一下：

<UICTFont: 0x14dd21b90> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 16.00pt
<UICTFont: 0x14de58bb0> font-family: "PingFangSC-Regular"; font-weight: normal; font-style: normal; font-size: 16.00pt

系统默认字体的font-family是".SFUI-Regular"（.SF是San Francisco的简写），苹方字体的font-family是"PingFangSC-Regular"。这样明显的证据摆在面前，为啥设计师说默认系统字体就是苹方字体呢？
“怎么说呢，手机一个字体包括中文和英文，对不？就问题来说：San Francisco是苹方字体的英文部分，中文部分叫苹方黑体。”

补充

San Francisco是苹方字体的英文部分，中文部分叫苹方黑体。但是，两者之间是有差距的。比如对数字的显示，平方字体显示的数字与前后汉字更加紧凑，但是San Francisco与前后汉字之间会有一定间隔。

附录：

    UIFont *font1 = [UIFont systemFontOfSize:16];
    UIFont *font2 = [UIFont boldSystemFontOfSize:16];
    UIFont *font3 = [UIFont italicSystemFontOfSize:16];

    UIFont *font4 = [UIFont systemFontOfSize:16 weight:UIFontWeightRegular];
    UIFont *font5 = [UIFont systemFontOfSize:16 weight:UIFontWeightMedium];
    UIFont *font6 = [UIFont systemFontOfSize:16 weight:UIFontWeightSemibold];

打印：
<UICTFont: 0x10a91cbe0> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 16.00pt
<UICTFont: 0x10a930de0> font-family: ".SFUI-Semibold"; font-weight: bold; font-style: normal; font-size: 16.00pt
<UICTFont: 0x10a92f650> font-family: ".SFUI-RegularItalic"; font-weight: normal; font-style: italic; font-size: 16.00pt

<UICTFont: 0x105a01f80> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 16.00pt
<UICTFont: 0x105943960> font-family: ".SFUI-Medium"; font-weight: normal; font-style: normal; font-size: 16.00pt
<UICTFont: 0x1059443c0> font-family: ".SFUI-Semibold"; font-weight: bold; font-style: normal; font-size: 16.00pt