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我尝试在一个 S3 类上定义一个类 Ops 继承，该类是一个列表，并且在列表中有一个时间序列。

tsnewobject_a <- structure(list(data=ts(1:10,frequency=4,start=2010)),
                           class="newclass")
tsnewobject_b <- structure(list(data=ts(10:1,frequency=4,start=2010)),
                           class="newclass")

## Step 1 : with S3 only (note : I don't want to modify Ops.ts)

Ops.newclass <- function(e1,e2) {
  if (inherits(e1,"newclass")) e1 <- e1$data
  if (inherits(e2,"newclass")) e2 <- e2$data
  get(.Generic)(e1,e2)
}

tsnewobject_a+tsnewobject_b
#      Qtr1 Qtr2 Qtr3 Qtr4
# 2010   11   11   11   11
# 2011   11   11   11   11
# 2012   11   11 

# It works !

tsnewobject_a+1
#      Qtr1 Qtr2 Qtr3 Qtr4
# 2010    2    3    4    5
# 2011    6    7    8    9
# 2012   10   11 

# It works !

1+tsnewobject_a
#      Qtr1 Qtr2 Qtr3 Qtr4
# 2010    2    3    4    5
# 2011    6    7    8    9
# 2012   10   11 

# It works !

tsnewobject_a+ts(1:10,frequency=4,start=2010)
# Error in tsnewobject_a + ts(1:10, frequency = 4, start = 2010) : 
#   non-numeric argument to binary operator
# In addition: Warning message:
# Incompatible methods ("Ops.newclass", "Ops.ts") for "+" 

# It doesn't work (it's expected)

ts(1:10,frequency=4,start=2010)+tsnewobject_a
# Error in ts(1:10, frequency = 4, start = 2010) + tsnewobject_a : 
#   non-numeric argument to binary operator
# In addition: Warning message:
# Incompatible methods ("Ops.ts", "Ops.newclass") for "+" 

# It doesn't work (it's expected)

由于 S3 double dispatch，它不适用于简单的方法。因为我不想覆盖 Ops.ts（它是为了一个包），所以我必须找到一些东西。

## Step 2 : setOldClass to complete S3 with a small s4 fix

setOldClass("newclass")
setMethod("Ops",signature = c("newclass","ts"),function(e1,e2) callGeneric(e1$data,e2))
setMethod("Ops",signature = c("ts","newclass"),function(e1,e2) callGeneric(e1,e2$data))

tsnewobject_a+ts(1:10,frequency=4,start=2010)

# Error in tsnewobject_a + ts(1:10, frequency = 4, start = 2010) : 
#   non-numeric argument to binary operator
# In addition: Warning message:
# Incompatible methods ("Ops.newclass", "Ops.ts") for "+" 

# Still doesn't work

ts(1:10,frequency=4,start=2010)+tsnewobject_a

# Error in ts(1:10, frequency = 4, start = 2010) + tsnewobject_a : 
#   non-numeric argument to binary operator
# In addition: Warning message:
# Incompatible methods ("Ops.ts", "Ops.newclass") for "+" 

# Still doesn't work

对我来说这似乎很奇怪，因为 Ops 是 S4 组通用的。它不应该调用可用的 S4 方法，然后，如果没有，就转到 S3 吗？会发生什么以及如何解决？

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