May be null could be considered to be a singleton type two. In my possibly wrong understanding, PHP has three singleton types, not just two.
ใทใณใฐใซใใณๅใฏใใใ ใฒใจใคใฎๅคใฎใฟใๅใๅ
ฅใใๅใงใใ
PHP ใฏใตใใคใฎใทใณใฐใซใใณๅใใตใใผใใใฆใใพใใ
PHP 8.0.0 ไปฅ้ใงใตใใผใใใใ false ๅใจใ
PHP 8.2.0 ไปฅ้ใงใตใใผใใใใ true ๅใงใใ
PHP 8.2.0 ใใๅใฎใใผใธใงใณใงใฏใ falseๅใฏ union ๅ ใฎไธ้จใจใใฆใฎใฟไฝฟใใๅใงใใใ
ๆณจๆ: ใซในใฟใ ใฎใทใณใฐใซใใณๅใๅฎ็พฉใใใใจใฏใงใใพใใใ ใใใใใๅ ดๅใๅๆๅ(Enum) ใไฝฟใใใจใๆค่จใใฆใใ ใใใ
May be null could be considered to be a singleton type two. In my possibly wrong understanding, PHP has three singleton types, not just two.