# Block\_given? in defined method

**URL:** <https://www.ruby-forum.com/t/block-given-in-defined-method/137974>\
**Category:** Development\
**Created:** [May 19, 2008, 6:33am UTC](https://www.ruby-forum.com/t/block-given-in-defined-method/137974 "2008-05-19T06:33:18Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![SASADA\_Koichi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f1d935/32.png) [@SASADA\_Koichi](https://www.ruby-forum.com/u/SASADA_Koichi)\
**Post date:** [May 19, 2008, 6:33am UTC](https://www.ruby-forum.com/t/block-given-in-defined-method/137974/1 "2008-05-19T06:33:18Z")

</div>

e$B!!$5$5$@$G$9!%e(B

e$B!!e(Bblock\_given? e$B$r!$e(Bdefine\_method  
e$B$GDj5A$5$l$?$b$N$KE,MQ$5$l$k$H$\*$+e(B  
e$B$7$J$3$H$K$J$k!$$H$$$&;XE&$K$D$$$F65$($F2\<$5$$!%e(B

e$B!!$3$N;XE&$O!$e(Bbootstraptest/test\_knwonbug.rb  
e$B$K%F%9%H%1!\<%9$,$"$j$^$9!%e(B

assert\_equal ‘ok’, %q{  
class C  
define\_method(:foo) {  
if block\_given?  
:ok  
else  
:ng  
end  
}  
end  
C.new.foo {}  
}, ‘[ruby-core:14813]’

assert\_equal ‘ok’, %q{  
class C  
define\_method(:foo) {  
if block\_given?  
:ng  
else  
:ok  
end  
}  
end  
C.new.foo  
}, ‘[ruby-core:14813]’

e$B!!e(Bblock\_given? e$B$O!$B?J,e(B yield e$B$d$ie(B Proc.new  
e$B$J$I$,=PMh$k$+$I$&$+$r3Ne(B  
e$BG’$9$k$?$a$N$b$N$@$H;W$&$N$G$9$,!$e(Bdefine\_method  
e$B$GDj5A$7$?%a%=%C%I$Ge(B  
e$B$O$I$A$i$b=PMh$^$;$s!J8=\>u$G$O!K!%$J$N$G!$e(Bblock\_given?  
e$B$b!$$=$NMQESe(B  
e$B$K$O;H$($J$$0J\>e!$%F%9%H%1!\<%9$N$h$&$K$9$k$N$O$^$:$$$H;W$&$N$G$9$,!$e(B  
e$B$$$+$,$G$7$g$&$+!%e(B

e$B!!$3$N\>l9g!$$I$A$i$be(B false e$B$K$J$k$Y$-$J$h$&$J5$$,$7$^$9!%e(B

---

<div class="post-metadata">

**Author:** ![SASADA\_Koichi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f1d935/32.png) [@SASADA\_Koichi](https://www.ruby-forum.com/u/SASADA_Koichi)\
**Post date:** [May 19, 2008, 11:34am UTC](https://www.ruby-forum.com/t/block-given-in-defined-method/137974/2 "2008-05-19T11:34:58Z")

</div>

e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B

In message “Re: [ruby-dev:34747] block\_given? in defined method”  
on Mon, 19 May 2008 13:32:48 +0900, SASADA Koichi [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
writes:

|e$B!!e(Bblock\_given? e$B$r!$e(Bdefine\_method e$B$GDj5A$5$l$?$b$N$KE,MQ$5$l$k$H$\*$+e(B  
|e$B$7$J$3$H$K$J$k!$$H$$$&;XE&$K$D$$$F65$($F2\<$5$$!%e(B

|e$B!!e(Bblock\_given? e$B$O!$B?J,e(B yield e$B$d$ie(B Proc.new e$B$J$I$,=PMh$k$+$I$&$+$r3Ne(B  
|e$BG’$9$k$?$a$N$b$N$@$H;W$&$N$G$9$,!$e(Bdefine\_method e$B$GDj5A$7$?%a%=%C%I$Ge(B  
|e$B$O$I$A$i$b=PMh$^$;$s!J8=\>u$G$O!K!%$J$N$G!$e(Bblock\_given? e$B$b!$$=$NMQESe(B  
|e$B$K$O;H$($J$$0J\>e!$%F%9%H%1!\<%9$N$h$&$K$9$k$N$O$^$:$$$H;W$&$N$G$9$,!$e(B  
|e$B$$$+$,$G$7$g$&$+!%e(B

e$B$(!\<$H!"$G$-$J$$$s$G$7$?$C$1!#$=$l$rG’\<1$7$F$$$^$;$s$G$7$?!#e(B  
lambdae$B$O%V%m%C%/\<u$1IU$1$^$9$h$M!#$G!“e(Bdefine\_methode$B$GDj5A$5$le(B  
e$B$?%a%=%C%I$G$O$G$-$J$$$H8@$&$N$Oe$N?\<$$M}M3$,$”$k$s$G$7$ge(B  
e$B$&$+!#e(B

|e$B!!$3$N\>l9g!$$I$A$i$be(B false e$B$K$J$k$Y$-$J$h$&$J5$$,$7$^$9!%e(B

e$BBh0l$NA\*Br;h$Oe(Bdefine\_methode$B$GDj5A$5$l$?%a%=%C%I$+$i$be(Byielde$B$Ge(B  
e$B$-$F$[$7$$$s$G$9$,!"$J$s$i$+$N;v\>p$G$=$l$,2DG=$G$J$$$J$i$P!"e(B  
e$B$=$N\>l9g$ON\>J}e(Bfalsee$B$G$bNI$$$H;W$$$^$9!#e(B

```
                            e$B$^$D$b$He(B e$B$f$-$R$me(B /:|)

```

---

<div class="post-metadata">

**Author:** ![SASADA\_Koichi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f1d935/32.png) [@SASADA\_Koichi](https://www.ruby-forum.com/u/SASADA_Koichi)\
**Post date:** [May 19, 2008, 12:04pm UTC](https://www.ruby-forum.com/t/block-given-in-defined-method/137974/3 "2008-05-19T12:04:31Z")

</div>

e$B!!$5$5$@$G$9!%e(B

Yukihiro M. wrote:

> |e$B!!e(Bblock\_given? e$B$O!$B?J,e(B yield e$B$d$ie(B Proc.new e$B$J$I$,=PMh$k$+$I$&$+$r3Ne(B  
> |e$BG’$9$k$?$a$N$b$N$@$H;W$&$N$G$9$,!$e(Bdefine\_method e$B$GDj5A$7$?%a%=%C%I$Ge(B  
> |e$B$O$I$A$i$b=PMh$^$;$s!J8=\>u$G$O!K!%$J$N$G!$e(Bblock\_given? e$B$b!$$=$NMQESe(B  
> |e$B$K$O;H$($J$$0J\>e!$%F%9%H%1!\<%9$N$h$&$K$9$k$N$O$^$:$$$H;W$&$N$G$9$,!$e(B  
> |e$B$$$+$,$G$7$g$&$+!%e(B
> 
> e$B$(!\<$H!"$G$-$J$$$s$G$7$?$C$1!#$=$l$rG’\<1$7$F$$$^$;$s$G$7$?!#e(B  
> lambdae$B$O%V%m%C%/\<u$1IU$1$^$9$h$M!#$G!“e(Bdefine\_methode$B$GDj5A$5$le(B  
> e$B$?%a%=%C%I$G$O$G$-$J$$$H8@$&$N$Oe$N?\<$$M}M3$,$”$k$s$G$7$ge(B  
> e$B$&$+!#e(B

e$B!!e(Blambda e$B$He(B define\_method  
e$B$GDj5A$7$?%a%=%C%I!J0J2\<!$e(Bdme$B!K$OF1DxEY$K%Ve(B  
e$B%m%C%/$r\<u$1IU$1$^$9!%e(B

l = lambda{|&b|  
p b  
yield #=\> #\<LocalJumpError: no block given (yield)\>  
}

class C  
define\_method(:dm){|&b|  
p b  
yield #=\> #\<LocalJumpError: no block given (yield)\>  
}  
end

begin  
l.call{}  
rescue LocalJumpError =\> e  
p e  
end

begin  
C.new.dm{}  
rescue LocalJumpError =\> e  
p e  
end

e$B!!e(BYARV e$B$G$Oe(B yield  
e$B$NDj5A$r!$?7$7$$JQ?t%9%3!\<%W$r:n@.$9$k%?%$%\_%s%0$Ge(B  
e$BEO$5$l$?%V%m%C%/\>pJs$rMxMQ$7$F9T$&?7$7$$%9%3!\<%W$N:n@.!&\<B9T$H$7$F$$e(B  
e$B$^$9!%e(Bdefine\_method  
e$B$GDj5A$5$l$?%V%m%C%/$O!$8F$S=P$7$F$b?7$7$$%9%3!\<e(B  
e$B%W$O:n$i$J$$$?$a!J%V%m%C%/$N30$N%9%3!\<%W$r0z$-7Q$0$?$a!K!$e(Bdm  
e$B$KEO$7e(B  
e$B$?%V%m%C%/$OBP\>]$K$G$-$^$;$s!%$?$@$7!$%V%m%C%/$re(B block  
e$B0z?t!Je(B&be$B!K$Ge(B  
e$B\<u$1$k$3$H$,=PMh$k$N$G!$$=$l$r;H$\*$&$H$$$&J}?K$@$C$?$H;W$$$^$9!%e(B

e$B!!$3$N%k!\<%k$O!$7k6I$[$+$N%V%m%C%/$HF1$8$J$N$G!$$o$+$j$d$9$$$H8@$($ke(B  
e$B$+$H;W$$$^$9!%$D$^$j!$0J2\<$N$h$&$JNc$G$O!$e(Bsetup  
e$B$KEO$7$?%V%m%C%/$,8Fe(B  
e$B$P$l$^$9$,!$$3$l$O;zLL\>e!$B\>$N%V%m%C%/$He(B  
lambdae$B!$e(Bdefine\_method e$BEy$Ge(B  
e$BF1$85sF0$G$9!%e(B

class C  
end

def setup  
$l = lambda{|&b|  
p b  
yield #=\> block in main  
}

C.module\_eval{  
define\_method(:dm){|&b|  
p b  
yield #=\> block in main  
}  
}  
end

setup{  
puts “block in main”  
}

$l.call{}  
C.new.dm{}

e$B!!e(Bdefine\_method e$B$rFCJL07$$$9$k$N$J$i!$:G=i$+$ie(B define\_method  
e$B$r0U\<1e(B  
e$B$7$?:n$j$K$7$J$$$HB.EYE\*$KFq$7$$$+$J!$$H;W$$$^$9!%B.EY$r5$$K$7$J$$$Ne(B  
e$B$J$i!$$b$7$+$7$?$i$=$s$J$KFq$7$/$J$$$+$b$7$l$^$;$s!%e(B

# e$B$?$7$+!$$3$N$"$?$j$O5nG/!$L5M}$G$9!$4\*J[$7$F2\<$5$$!$e(B

# e$B$H8@$C$F$$$?$h$&$J5$$,$9$k!%e(B

> |e$B!!$3$N\>l9g!$$I$A$i$be(B false e$B$K$J$k$Y$-$J$h$&$J5$$,$7$^$9!%e(B
> 
> e$BBh0l$NA\*Br;h$Oe(Bdefine\_methode$B$GDj5A$5$l$?%a%=%C%I$+$i$be(Byielde$B$Ge(B  
> e$B$-$F$[$7$$$s$G$9$,!"$J$s$i$+$N;v\>p$G$=$l$,2DG=$G$J$$$J$i$P!"e(B  
> e$B$=$N\>l9g$ON\>J}e(Bfalsee$B$G$bNI$$$H;W$$$^$9!#e(B

e$B!!\>e5-$NM}M3$GG\<F@$7$F$b$i$($k$N$J$ie(B false  
e$B$K$"$o$;$k$h$&$K$7$^$9!%e(B  
e$B$=$&$G$J$/!$$d$O$je(B define\_method  
e$B$OFCJL07$$$7$m!$$H$$$&$3$H$@$C$?e(B  
e$B$i!$$b$&\>/$79M$($5$;$F2\<$5$$!%e(B

---

<div class="post-metadata">

**Author:** ![SASADA\_Koichi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f1d935/32.png) [@SASADA\_Koichi](https://www.ruby-forum.com/u/SASADA_Koichi)\
**Post date:** [May 19, 2008, 3:29pm UTC](https://www.ruby-forum.com/t/block-given-in-defined-method/137974/4 "2008-05-19T15:29:56Z")

</div>

e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B

In message “Re: [ruby-dev:34753] Re: block\_given? in defined method”  
on Mon, 19 May 2008 19:03:10 +0900, SASADA Koichi [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
writes:

|e$B!!e(Blambda e$B$He(B define\_method e$B$GDj5A$7$?%a%=%C%I!J0J2\<!$e(Bdme$B!K$OF1DxEY$K%Ve(B  
|e$B%m%C%/$r\<u$1IU$1$^$9!%e(B

e$B$^$H$a$k$H%V%m%C%/0z?t$H$7$F$OEO$k$1$I!“e(Byielde$B$O8F$Y$J$$$H$$e(B  
e$B$&$3$H$G$$$$$G$9$+!#$3$l$C$F!”$?$H$($P$=$N%V%m%C%/$N30B&$Ge(B  
yielde$B$,M-8z$@$C$?$i$=$C$A$,8F$P$l$k$H$$$&$3$H$G$$$$$G$9$+!)e(B

e$B3N$+$a$F$\_$l$P$$$$$N$+!#e(B

def foo  
l = lambda{|&b|  
p b  
p block\_given?  
yield  
}  
end

foo{p :foo}.call  
foo{p :foo}.call{p :bar}

e$B$r\<B9T$9$k$He(B

nil  
true  
:foo  
#Proc:0x8b8083c@/tmp/y.rb:9  
true  
:foo

e$B$G$9$+!#$J$k$[$I$M!“$”$k0UL#!“0l4S@-$,$”$k$H8@$($P$"$j$^$9$M!#e(B

|e$B!!$3$N%k!\<%k$O!$7k6I$[$+$N%V%m%C%/$HF1$8$J$N$G!$$o$+$j$d$9$$$H8@$($ke(B  
|e$B$+$H;W$$$^$9!%$D$^$j!$0J2\<$N$h$&$JNc$G$O!$e(Bsetup e$B$KEO$7$?%V%m%C%/$,8Fe(B  
|e$B$P$l$^$9$,!$$3$l$O;zLL\>e!$B\>$N%V%m%C%/$He(B lambdae$B!$e(Bdefine\_method e$BEy$Ge(B  
|e$BF1$85sF0$G$9!%e(B

|e$B!!\>e5-$NM}M3$GG\<F@$7$F$b$i$($k$N$J$ie(B false e$B$K$"$o$;$k$h$&$K$7$^$9!%e(B  
|e$B$=$&$G$J$/!$$d$O$je(B define\_method e$B$OFCJL07$$$7$m!$$H$$$&$3$H$@$C$?e(B  
|e$B$i!$$b$&\>/$79M$($5$;$F2\<$5$$!%e(B

e$BM}2r$7$^$7$?!#$3$l$G$$$$$s$8$c$J$$$G$7$g$&$+!#%F%9%H$b=q$-49e(B  
e$B$($F$/$@$5$$!#e(B

```
                            e$B$^$D$b$He(B e$B$f$-$R$me(B /:|)

```