概要
Rails で、0、''、nil、falseの扱われかたを調べてみたメモ
present?
!blank? と同義。
下記の条件の時にfalseを返す。参考記事
nil''-
' '(半角スペースのみ) -
[](空の配列) -
{}(空のハッシュ)
###########
# true
###########
val = 1
puts val.present? # => true
val = 0
puts val.present? # => true
val = true
puts val.present? # => true
###########
# false
###########
val = false
puts val.present? # => false
val = ''
puts val.present? # => false
val = ' ' # 半角スペース
puts val.present? # => false
val = nil
puts val.present? # => false
val = []
puts val.present? # => false
val = {}
puts val.present? # => false
zero?
zeroかどうか調べる。
string, booleanでは.zeroは使えず、エラーになる。
###########
# true
###########
val = 0
puts val.to_i.zero? # => true
val = ''
puts val.to_i.zero? # => true
val = nil
puts val.to_i.zero? # => true
# 文字列をto_iすると0になる
val = 'sample'
puts val.to_i # => 0
puts val.to_i.zero? # => true
# 半角スペースもstringと同じ
val = ' '
puts val.to_i # => 0
puts val.to_i.zero? # => true
###########
# false
###########
val = 1
puts val.to_i.zero? # => false
###########
# error
###########
# string
val = 'sample'
puts val.zero?
# => NoMethodError: undefined method `zero?' for "sample":String
# 半角スペースもstringと同じ
val = ' '
puts val.zero?
# => NoMethodError: undefined method `zero?' for " ":String
# boolean
val = true
puts val.zero?
# => NoMethodError: undefined method `zero?' for false:FalseClass
puts val.to_i.zero?
# => NoMethodError: undefined method `to_i' for true:TrueClass
# boolean
val = false
puts val.zero?
# => NoMethodError: undefined method `zero?' for false:FalseClass
puts val.to_i.zero?
# => NoMethodError: undefined method `to_i' for false:FalseClass
val = []
puts val.zero?
# => NoMethodError: undefined method `zero?' for []:Array
puts val.to_i.zero?
# => NoMethodError: undefined method `to_i' for []:Array
val = {}
puts val.zero?
# => NoMethodError: undefined method `zero?' for {}:Hash
puts val.to_i.zero?
# => NoMethodError: undefined method `to_i' for {}:Hash
boolean?
そんなメソッドはない。
下記の判定式で、booleanかどうか判定できる。
########################
# is true? or is false?
########################
val = true
puts val.is_a?(TrueClass) # => true
puts val.is_a?(FalseClass) # => false
val = false
puts val.is_a?(TrueClass) # => false
puts val.is_a?(FalseClass) # => true
########################
# is boolean? == true
########################
val = true
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => true
val = false
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => true
########################
# is boolean? == false
########################
val = 1
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = 0
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = ''
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = ' ' # 半角スペース
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = nil
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = 'sample'
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = []
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
val = {}
puts val.is_a?(FalseClass) || val.is_a?(TrueClass) # => false
以上